Hey, don't be scared to participate in a game jam. The worst that can happen is you submit a game that isn't very good. But who cares if you do? What's important is that you've made something, and in the making, you've learned something. That's what it's all about. 

You know how you get better at doing things? 

You get better at doing things by doing the things. You want to make games? Then make games, even if they're not very good, or you don't have much time, and your next game will be better and your next game will be even better. 

What I'm saying is, don't be afraid to participate, don't be afraid to submit whatever you have at the end of the jam, and be proud that you submitted anything and that you learned by working on what you did submit.