Wooden pieces, string, blunt scissors, glue,
all lay scattered over the carpet. Creating a mousetrap car was not an easy task.
At one point, the car slowly trolled ten feet, stirring a little celebration, but
that same point
reminded me that going twenty feet in under five seconds seemed impossible.
^How about replacing that with "at the same time reminded me..."
Nevertheless, I kept on trying different designs. If others can do it, I can do it too
This was my motivation to keep going. On the day of the race, I eagerly watched indescribable
cars take off from the starting line.
^I feel like indescribable isn't the right word to use.
I placed my front wheels on the starting tape, pulled back the mousetrap, and let it free. But
there was more to it than just sticks of wood.
^Try not to start a sentence with "but." Maybe "however" would be more suitable?
I realized that it wasn't because I was better at physics than everyone else
, but because I had the most will that enabled me to cross the finish line
^Try not to sound too arrogant.
At that time, as a late sophomore, if I thought I wouldn't be able to do something, I wouldn't even try doing it.
^This sounds a little choppy. Consider eliminating some words to make it flow more, or just revise the sentence altogether.
I had no idea what I was missing. English was never my best subject.
Though this is a pretty good essay, I think it would sound alot better if you added more transistional sentences/words at the end of each paragraph to make it flow more.