Try this…
peel a corner off, maybe exposing 3 to 4 inches of adhesive, ( you should now have a triangular portion of adhesive exposed) .... put it the felt in the box while holding that corner up, from being adhered to the surface. Positon the rest of the felt like you want it….then press the corner into place….then lift the felt some pulling more backing away ( 5 to 6 more inches ) push it down, and continue until the piece is all adhered. ( maybe peeling and sticking 5 times or so) It sounds more difficult than it is, but in fact it works great.
I have owned and operated a large portrait studio for 35 years, and we used to have our own color lab. We used self adhesive board for our large prints. Without using this method, you had no hope of ever getting the photo on the board in the right position and without flaws…I have used it for all “sticker” involved projects I have used.