I agree...its all the seam allowances, but I gotta tell you girls not yet at this point....get ready because she is one heavy heavy girl! I put a "protective" layer of cardboard on our kitchen table, clamp the back down and then lay the top on...spray baste & pin...then release and slide it to another section, reclamp the back on the side that is loose..the weight of the thing pulls the other side taunt, spray baste and pin the next section and so on. I neglected to flip it over in between sections though so the back isn't as tight as I would like. I'm going to sew a vertical and a horizontal to section it and then re-smooth the back and repin it before I go further.
Debbie, I'm not sure how you are planning to quilt yours. I guess you could just use like a sheet between them or something very lightweight but you will still be dealing with those thick layers of seam allowances. They are tough to deal with on 1 top thickness, I'm not sure how you would handle that on 2 tops together. Yours might not be quite as thick though because you didn't paper piece. That might make a difference. Reversible would be lovely if you can figure out how to deal with that issue. The only other thing I can think of is that you would have to flip it to be able to admire them both whereas if you had 2 quilts, well, you could..well I dunno..how many kids do you have that would want the quilt????