Years ago I would scarf plywood and/or trim pieces. I no longer do that preferring to use a butt joint instead. It's much faster, easier, and plenty strong...very much stronger than a poorly done scarf (good true scarfs are hard). I use only one layer of 6oz cloth on each side though. The plywood will usually fair nicely, but if it doesn't I have no problem with sanding, or tweaking to get a nice curve. Rather than holding fast to exact dimensions I tend to allow the wood to do more or less what it wants to do...as long as it is close and fair. I use as few wire stitches as I can, but do adust while stitching. I have never had any problems in aligning the butt joints. I do cut trim pieces, or other pieces on an angle only for looks when needed. In your case, since everything is already cut, you might consider removing some, or all of the tape you have until you can get a fair bend. It's really better not to have lots of narrow tape under the main cloth. It leaves ridges where you might cut through the main fiberglass cloth while sanding or scraping and cause weakness. If you need more strength add the tape after the main cloth, but that's probably another area to think about. Remember that there are as many different right ways to do things as there are wrong ways. It just seems that the wrong ways jump out at you. Good luck, and have fun.