cat to exhaust problem

yesterday a friend and i installed my greddy evo catback..we used air tools so unscrewing was quick..the thing is..the cat has 3 screws sticking out where it connects to exhaust pipe..unscrewing the bolts..half of the bottom 2 bolts broke off along with the screw..and we were .left with the top one..im now pretty sure there has to be leaking since only 1 of 3 is screwed on tightly..the bottom 2 arent..what can i do? replace the cat?