wow dood that sucks that it rounded off... try slamming in a tight 12point on the rounded bolt and keep slamming it the shock of you slamming it probably will knock it loose
then pray to god the 12 point has a good enough grip and try loosening it.... dont use the impact when u do this itll just round off the bolt more... when i did my stillens... i almost rounded off the bolt.... luckily it gave out b4 it did... these bolts are a pain in the f*ckin ***... i can only imagine the headers...