Don't worry too much. Jams are about learning something new and enjoying the experience! I'm not saying you shouldn't be worried at all. But while you worry and stress, I hope you are content and proud of what you make.
And plus, I'm sure your skills aren't That bad. Maybe your just not giving yourself enough credit for what you've accomplished throughout your game dev journey.
But anyways, I wish you a very good luck and remember to enjoy the experience :D