Failed collage and lessons learned

I was trying to create a collage for a project, but it turned out really bad. No, the right side is not wonky, it was the way I scanned it. The big problem is (as I'm sure most rubber stampers know), there are different surfaces that I tried to stamp over. Had I simply stamped on tissue paper, I think I could have used a white glue or gel medium to adhere the tissue paper and hide the various lines created by the different paper thicknesses. The tissue would also have ensured that the bird (which is mounted) would have been in the correct place on the collage, something I found nearly impossible to accomplish due to the mounting.

I will try this technique again, though, now that I know what to try next time. Size of the collage is 4 X 4, which is really small in my world.