Hi Mikey, it's your first game jam which can be pretty tough on you all you need to do is spend time thinking about the theme and how you'll incorporate it into the core mechanic of your game think of something clever and crazy. Once you've wrapped your head around it. Focus on finishing the core mechanic. Think of what you want your game to be like and start building from that. If the game is about jumping make your you finish perfecting the jump mechanic then you build a game around that. You could add elements like enemies and obstacles and power ups not to make the game seem bulky but to in some way aid the core mechanic like a power-up that makes you jump higher won't help at all instead you can take that and twist it with a clever drawback that makes the player consider their options and desicions. Something fun yet challanging.
JUST REMEMBER
BUILD AROUND YOUR CORE MECHANIC.
I would also like to know which engine you use to develop.
Thanks.