Do I need to change the stem?
 

I received my first bike today, got it assembled. The guy at the shop, asked me if I got a 58cm just by looking at me, I was fitted for a 54 at Performance, and I got a 53.5cm, I did put all my measurements on Competitive Cyclist and it's calling for a 54cm top tube.

After The bike was assembled, the guy was surprised as it seemed like the bike fits me except the stem which is 90mm , CC calls for 100mm. My question is should I get say a 120mm stem to make up for the 10mm short in the top tube. CC saddle handlebar is 53cm while it's actually 49cm on my bike. My understanding is that longer stem will resolve this issue.

I took this picture, in which to my novice eyes looks like I'm too big for the bike at least my upper body.

Any input is greatly appreciated.

https://imgur.com/HbpcLao

https://imgur.com/HbpcLao

I'm also thinking maybe I have to raise the saddle a tiny bit.

1st question is = How did the first ride feel?

you said it's your first bike.

I didnt take it on the road yet, went on a 1 mile ride, didn't feel that it was small or anything, too easy on the hardest gear (46-11) maybe because of the 170mm crankset? I'm a total Noob, don't know any better.

Hugely unlikely.
You're not saying what wheel size you have. But If its 26" or bigger a 46/11 will get someone with average pedalling technique to about 30 mph or a bit above before spinning out.
Bicycling is more about stamina than strength. General recommendation is to keep a cadence - pedalling pace - of 80-100 rpm.
Well, we've all been there.
Thing is to start out with a bit of humbleness.
You need a decent mileage/saddle hours before being able to tell with confidence that it's the bike that needs changing.
In the beginning you're better off working on riding technique rather than ride technology.
If you're new to riding, this might feel fast and too light.
But it is the way to do it.
No.
165-175 mm is considered the "standard" lengths for cranks, with the majority found in the 170-175 mm range.
Longer cranks will make a gear feel lighter to turn. And yours aren't particularly long.
This is a far more likely explanation. You don't know how it's supposed to feel like yet.

To put some context behind this, 30mph is equivalent to 0.5 miles/minute or 2640 feet per minute.

In an ideal world, a 46/11 ratio means notionally that every revolution of your crankset in that gear means the wheel will rotate 4.18 times, and the linear distance it will roll will be approximately 2100mm times 4.18 (or 8782mm, or 28.8 feet.

Now, you can divide the 2640 feet per minute you want to go by the feet per revolution your gear ratio sends you, to estimate that you need 91 and change revolutions per minute of your crank to go 30 miles per hour.

In reality, this doesn't work quite so well due to mechanical and environmental losses in the system, but it's a rough idea.

Also in reality, it's quite hard for a lot of people to pedal a bike at that gear ratio with an RPM of 90.

New rider?, don't worry about crank length.

1. Avoid all contact with cars.
2. Keep the rubber side down.
3. Enjoy the days on the bike.
4. If your butt hurts during the first month (or 2), no saddle will fix it completely.
5. Learn to shift at the right time
6. Practice riding a straight line on the road, even when you reach for a bottle or turn your head.
7. Relax your shoulders, arms and hands - Now really relax shoulders, arms, and hands.
8. Get out of the saddle regularly.
9. Breathe more deeply.

Lots to learn before crank length.
Sorry, but i can't see the pics, so i know my answer is incomplete.

For roadies and people riding longer distances or faster speeds, clipless pedals and shoes make it sooo much easier.

The answer to your question is "Maybe". Your first priority should be is to get some miles underneath you before you start worrying about changing stems. Have fun on your bike and in a few months, get a professional fit. They will dial in your bike for comfort