No, that doesn’t sound right. There is no missing opening curly brace.
Line 44 is a one line else statement in PHP. No opening or closing curly brace is needed. The closing curly brace on line 49 goes with the opening curly brace on line 37.
Tons of people use download.php without any edits. You should not need to edit anything for basic functionality.
That said, I’m not 100% certain that multiple urls (checkboxes) works properly with hide/mask and/or expiration (so you may end up needing to make mods). I can’t quite remember. I know that I ended up making some mods for some reason that I can’t recall any more.
What I would do if I were you is put download.php back like it was and then get it working with the defaults. Don’t do hide/mask, definitely don’t do expiration. Just get the default stuff working. Once it’s working, try hide/mask and see if it still works. If so, then try expiration … note that once things get in the database then things can get weird, so you may already be in a weird state. If I were in your shoes, I would start over with a completely new form (to get a new form id), make completely new downloads (to get new download ids) and I would use new filenames too just to be safe, then make a completely new page in wordpress and put your new shortcode in that new page and then test. It’s important that you don’t accidentally use any of the old stuff — if you do, then it might end up pulling old stuff from the database and mess up.