That’s why one is always asked to save all important data at least on two different drives or places. So, I hope you can learn a lesson to back up everything well all the time.
But, now, in order to rescue your stuffs there, you’d better do not format this USB and also do not overwrite this USB.
And then, check whether all of your stuffs there can be retrieved back with the help of some data recovery tools, like Recuva, 4Card Recovery, PhotoRec and more.
No matter which one you want to try, always act carefully and save all restored stuffs on a completely different drive or USB in case of further data loss.
I hope these words could give you some help.