Usually if you just place the key where it belongs and press on it (rather hard) it will noticably snap back into place. It should feel normal after you do that. If it doesn't, you broke part of the plastic clips that holds it into place.
Well, the one key goes on if I push hard, but the one side sticks up more than it should. Maybe there's a certain way you have to push it on? The plastic clips on the bottom look alright. The other key actually had the rubber pad come off as well. Could I glue it back on?