There are a lot of factors. The long drive, the heat, the long warm up (this last bit doesn't sound right if it's 90 deg), they all work against you.
I've never been one to enjoy heat. I need to stay cooler to do okay on the bike - even 80 deg is uncomfortable for me. I also know that if my legs are cold (i.e. I've been sitting in AC and my skin is cold to touch) that I race horribly. I always end up dehydrated when it's warm. Finally if it's a while between races or there's a long drive (over 1.5 or 2 hours) then I'm usually a bit "off" when I start, i.e. sluggish. Some of my tactics to help me deal with this stuff:
Staying cooler - Podium Ice bottles (not even the Chill), filled with ice cubes and water at home, then put in cooler. I bring 2-4 other bottles of ice and water but just stick them in the cooler (I have two Chills, they're relegated to "drinking on the way" duty). I stay hydrated and stay cool by drinking cold water.
AC - I either cover my legs or reduce AC coldness. I try and keep my leg veins from constricting. "Pleasantly warm" describes the feeling in my legs. Usually in a nicely air conditioned car I'll put a jacket over my legs or wear sweatpants.
Long time between races or long drive to a race - sugar, caffeine, and stay focused on racing. Warm up a little if it's warm, a lot if your legs feel like cold blocks of wood. That's a lot so read on.
I try and eat some higher calorie food, with more sugar than anything else the closer I get to the race. If it's a while to go I prefer a high calorie snack like a muffin and a coffee, if it's closer then it's more sugary like a gel or three or a Pop Tart. Yesterday I had a race at noon and another at 3. I like to eat a relatively large meal at 3 hours to go, and we had a short drive (30 min). I ate as late as possible for me, about 8:30 AM (I was up at 4? due to the baby, and ate a meal at that point). After my race at noon it was raining and I wasn't sure if I was going to race at 3. At 2:20 the sun was coming out, it was getting hot for me (80?), so I decided to register for the second race, had 2 GUs, 1 pack of Bloks, and bought two cans of Coke, poured them both in a Podium Chill bottle (it wasn't that warm and we'd used the water from the Chill for the baby). I drank half of it before the start, also drank almost a bottle of water. During the race the sun came out and I had a massive headache (very unusual for me), I had to start dumping water on me, ran out of Coke, etc. Keep in mind that at 3 PM I hadn't eaten anything else since about 9:15 (when I finished breakfast - eggs, bacon, toast, coffee). The sugar got me jumpstarted after me not being keen to get dressed to race for almost 2 hours. My warmup for the second race consisted of rolling from the car to our "base" at the finish area, pinning on my number, and lining up. I went off the front 1/2 lap later.
When I do Bethel (i.e. promote) I'm up at 5:15, work the race from 6-12:30, jump on the bike at 12:30 and race until I can't anymore, usually 1:30 (end of the Cat 3-4 race) or 2-4 PM (beginning/middle/end of P123 race). I can't eat much at 5:15 (no time) so I have an egg sandwich (usually two) in the long morning, a muffin, maybe a snack or two (Hammer bar or gel or something). I stay on edge the whole day due to the fact that I'm responsible for the race and I literally get zero warm up (I timed my warmups in 2011? and they were usually 0 to 45 seconds - it takes about 15 seconds to ride from registration to the line, and if I forget something I have to ride back, and if it's busy I walk my bike out). Nonetheless I manage to do well I mention all this because if you keep your mind busy you'll stay amped. This can mean reviewing cam footage of the race from prior years. It's become prevalent enough that on the way to a crit in SoCal
I'd never done before I could watch a cam clip from the prior year
while in the car (thanks to a wireless broadband connection).
If you have teammates or friends you can talk about the race. If not you can scout the course, walk or ride it, with the intent of checking out corners etc (if this is a crit/circuit). I learn/retain things visually so in the old days I used to draw a rough diagram of the course and put in what I thought were pertinent features, and thought of ways I would use (hills, corners, descents) or avoid (potholes, glass, sudden narrowing, etc) them. This helped me retain stuff so that in the initial part of the race I had something to think about. I also came up with a plan. People who know me will laugh because my plan is now "sit in and wait for sprint" but back then I had to consciously make that decision, it wasn't automatic. I also learned a lot of courses this way, which now, because the same courses get used all the time, it's not really an issue anymore. Sometimes my plan would be to work for someone else so I'd sacrifice
By staying involved with the race before you line up you can focus on the race. Don't worry (too much) about your significant other or work or whatever, not until after your race.
Finally there may be an element of burn out or fatigue here; for a new racer it's probably fatigue rather than burn out. If you don't want to race there's probably a reason for it. Training too much (I know guys that show up at a crit the day after doing 100 mi whereas they normally train 20-30 mi at a time; I did the Red Trolley Crit after a super hard week of training so I was incredibly fatigued), not recovering enough (including getting enough sleep, stressing due to work/relationships, regularly staying out too late), being too high strung driving (I once arrived at a race totally exhausted - as a 16 year old driver I thought it was safer to sit close enough to the car in front so I could see out their windshield, but sitting 5 feet off another car's bumper at 70 mph took so much energy I'd arrive at races mentally drained; now I am a really mellow driver on the way to races or I let someone else drive), etc etc etc.