When I first built my stripper, I decided to get the 'glass on the inside right after getting it on the outside, and then worked on finishing (sanding) after that. After I cracked it up, and while I was repairing it, we had a seasonal change, and the changes in relative humidity seemed to change the shape of the hull, making it want to sit wider or narrower than expected. I don't know how much this can affect things, but my boat (a solo) got almost 2" wider during a storm, than when it was nice & dry. Of course, final width is determined by thwart length, but you risk stressing the outer glass if you pull it in too much. Just a thought.... Hopefully someone with greater knowledge than I will shed some light on these observations.
Be patient, work carefully. It'll be beautiful, and well worth all that sanding horror!