I've done the same thing in the past, and Recuva has worked wonders. Don't use the USB drive anymore, and be sure to run Recuva from a different drive than the one you want to pull files from.
Trying to recover some files which Recuva can see - and despite is suggesting saving those files to another drive there's no option to do so - just one button 'Recover'
Edit - i see it lets you choose *after* you click recover