The Book Of Fundamentals

[Punk-A-Cat]

I don't know if it makes any difference but I use a lap tray (just a bit of hardboard at the moment) which ends up angled on my lap - it puts less strain on my wrist is why I started. Maybe you could get a flat surface and prop it up on an angle on the desk to draw on?
I would be picking the paper up, flipping it upside down, looking at in a mirror - all the usual tricks to try and catch warping in the basic construction before you do any rendering.