Code doesn't work in Theme Folder?

Long story short, I tried to add a Twitter Timeline plugin to my WP site, it wasn’t compatible, and now the code is broken so the site won’t work. I still have the window open where I can edit the code for the theme, and I downloaded the same theme again and posted the correct code in it, but it still doesn’t work.

Am I going to have to go through FTP to get this all straightened out? (I’m desperately trying to get the login information for FileZilla since I didn’t build this site, and so far I haven’t found anything.) I just wanted to double check and make sure that I’m not overlooking a simple fix for what I did.