Thanks boys. That's what I thought. I'm understanding from starting this that it is important to pay attention to good workmanship, but that if one gets too OCD then the pace of work will make completing the project a very distant dream if not an impossibility.
This is but a small problem. The thing that PO's me is that it's a well documented gotcha. Until the skin is in place though it'd difficult to tell if you rounded the ribs enough and by then it is too late.
One thing I had considered was centering a bucking bar behind and giving it a short couple taps with a flush face rivet gun. I don't know if that's been tried before but it sounds plausible to me.