you forgot to include rolling resistance of the tires, probably have to take into account the air density to get a more accurate F resulting from air… shit if you actually know what you are doing in regards to this, but I doubt many people would want to actually sit down and do the math to this, and you might want a program like mathcad where you only have to define the variables.
EDIT: and you have to also take into account your lack of reaction times for the timing system