I had pretty good luck with a Future bath to solve a similar problem. Grab a corner of the canopy with the smallest clip you can find but be carefull; if you get Future between the clamp and the canopy it will slip out of the clamp. Dip it in some Future and blot one corner to remove the excess or you'll end up with a hardened drop of acrylic on the bottom of the canopy. Put it aside overnight and watch that crack disappear.