This is why I strongly suggest that people DON'T try to repair their own phones. It costs more to do it yourself.
Now find a shop that will work on a phone that you damaged and pay them to fix it. (Most shops won't ]because if something else breaks, you'll blame them], those that will may not guarantee the work unless you pay for a total analysis of the phone, and the repair usually ends up costing more than buying a good used S3 would.)
In my shops, no one touched a customer's phone for internal repair until he had "repaired" 6 phones (that didn't pay to fix) successfully. Things like the first 2 phones you try to replace the glass on usually result in a damaged screen. Or forgetting to put one screw back inside - the one that grounds a critical shield. Or, like you did, not heating the entire area uniformly. After you've done 6 right (which means anywhere from 10-20 altogether, depending on how fast you learn), you probably won't make mistakes like that. Just learning how hot is hot enough but not too hot takes a phone or two.