Sorry, but you are not allowed to make assets specifically for the jam, prior to the start date of the jam.
If you don't think you can make music that meets your standards within the 48 hour limit of the jam, then you're probably already overscoping the work you plan on doing during the 48 hours.
I suggest you either think about the shortest possible loop you can make that would work for a game, and practice by making a few different songs at that size before the jam begins, or looking for premade music from other people.
I hope that helps. 👍