Make sure it's a thin layer of resin to start. If you use too much, the paper soaks up the moisture and that is what causes the warping. After that initial layer is dry, you can add more layers inside and out......make sure that each layer has thoroughly dried before adding the next. As far as fiberglassing goes, you have mats or weave design. You should cut enough strips to more than cover the area you will be working on. Cut them into different sizes but not too large, they are sometimes hard to work with if too large. I don't use larger than a 3" x 3" square or 2" x 4" rectangle when working an area w/ a lot of indents or crevasses but large flat open sections.......could be covered in one go.....just overlap the edges. As far as rounding the edges....elbow grease.......or get yourself a power sander and go to town. If you find that you have a pocket of air while sanding which leaves a hole, fill it w/ either resin or bondo.