Hello Katie E, you are 100% allowed to expand on your game that you will be making for the jam. Game jams are just a helping hand to give ideas to someone so they can create a game. For example Oneshot a rpg maker game was created for a jam and was later expand on and is a commercial game. Also like Pixality said it's your content! So you have the final say of what you are going to do with it.
^^b I do hope you have a fun time in this jam btw.