Tapco rivets too short?

Guys I went ahead while ordering a center support bushing from Tapco, and got a set of rivets. I decided to go ahead and use them on my first build. However, after setting them in the rear trunnion, they barely expand past the receiver. I thought that they had expanded far enough over the edges too hold, but yesterday I found out that the most frontward one, had barely popped behind the receiver. I could hardly tell it happened. I was able to tap it back through the wall of the receiver, but of course it isn't very tight.The rear rivet is mushroomed far enough to hold though. What would your recommendations be to fix this. I was thinking I could, redo this rivet and the rear, but this would require shaving off both ends and removing the entire rear trunnion and then drilling out the rivets(PITA!!). Or, tapping the holes and screw into the existing rivets in the rear. Last, try to beat the hell out of the head some more to expand it. I don't know how much the latter will do though. If I screw it, the entire gun will be made out of rivets except for these. Sucks to get this far and have to use screws. But, grinding the heads off and hammering the rear trunnion out will be a pain too. Not to mention drilling the rivets out the rear trunnion. Your opinions would be great! Winn I know you've got a great answer for me this evening.