I removed the hitch and still was unable to fit the carriage bolts through the access hole. I'm still not sure how others got theirs to fit (aside from grinding the heads off).
So, I went to a hardware store and picked up some 3/8"x1.5" carriage bolts/washers/nuts. I was able to fit these bolts through the access hole and use them to tighten the sides of the hitch. These are slightly smaller than the bolts that came with the kit, but at least they fit, and I feel more comfortable using them than nothing at all on the sides.
Other than the carriage bolt issue, I do like the hitch, and like others have said it leaves plenty of clearance. Even with my Thule bike hitch installed, there is enough clearance to backup from my driveway to the street without nicking the ground, something my previous vehicle had a problem with.