Can't make any assumptions but most crashes are greatly contributed to by fatigue. So first piece of advice would be to acknowledge when you are tired and take proper precautions.
Also, I see you're preparing to ride with a small lane of travel but simply riding and getting a good feel for the bike is going to be about as good of preparation as trying to stay in a small lane. I know that's a lot easier to say after you've fallen, because it wouldn't really apply if nothing bad happened. But doing what you did isn't going to help you much, it'll just assess where your control of the bike is at.
Having ridden a BMX bike when I was younger and mountain bike more recently, I had to adjust to riding a road bike. The small tires make handling very touchy and make it a lot easier to take a spill. I've ridden off the trail a couple times on accident and haven't fallen but I feel in danger when it happens. When you accidentally get off the trail, treat it somewhat like you would losing control in a car (hydroplaning, driving on snow/ice, flat tire): try to go as straight as possible as you work toward recovery.
Have you ever crossed railroad tracks or received advice about doing so? I've been on two organized rides (Flying Wheels and STP) and both had railroad tracks and both had crashes at the railroad tracks. Not sure that applies to your crashing, but it might for the second crash. If the front wheel doesn't have enough momentum to get up over the curb it will follow the line of the curb which will most likely cause you to crash. And of course it will take less momentum to get over the "curb" the closer you are to a perpendicular approach.