I also tried peddling around in reverse to see how it would work. Not bad as long as you don't go too fast, at which time your rudder becomes susceptible to slamming to one side whereupon you lose control. Nevertheless, fun for a change. In your case, you actually found some practical use for reverse -- that's forward thinking!
You can check your masts -- if they wiggle or twist, they're still not installed correctly. As to the clew position, I like about 1/8 inch into the outhaul; check it the first few times to make sure the clew adjustment nut position is stable. If not, a drop of Lock Tite (blue) should help.