No. You can't reupload to the jam. However I do believe you can reupload to your own profile but you'd have to keep the current version in the jam. However I could be wrong about the upload to your own profile thing so double check that.
In the future I recommend finding a large amount of beta testers and testing a day or so early.
My team found about 20 beta testers from a Harry Potter discord we were in but we ran into the issue of testing about 1 hour to go.
It's good to get a good schedule going and leave enough time for testing!
