Botero, if you can get ahold of a fixed gear bike, that would do wonders for your spinning abilities. I started racing on a velodrome, so that took care of it for me.
As a junior, I never lost a sprint due to gear restrictions. The exception, however, is when a junior enters in a senior race. Not much of a problem in flat crits, but anything with a hill leaves the junior with no way to keep up on the descents.