I'm having a hard time picturing what you're describing, but is sounds like your bike is too small for the lock. This is hardly unusual...u-locks offer good security, but are somewhat inconvenient. I've given up on mounting clamps, since I've never found a design that really works. I normally have a trunk bag or pannier that carries the lock, but I've seen a number of people who simply slide the lock straight into the rear rack, and that appears to be quite effective.