so the glue didn't really stick to the cardboard... at all. i should have got stronger glue but it would have been waaaay more expensive.
so i ended up just gluing a bunch of the cardstock together in a kind of mesh pattern to make it stronger. i reinforced the back of it with tape, duct tape on the frame and scotch tape on all of the seams, then i'll be putting some packing tape right down the middle.
for the grid paper, i just ordered poster-sized grid paper instead. it was relatively cheap and it will make it so i don't have to perfectly align a bunch of smaller ones. instead of needing to align like 9-12 papers it will only be like, 2 or 3.