What did I do wrong?

I attempted the method for doing larger perler pieces (posted by u/burner_account_9975) and although I spent a few seconds pressing as hard as I could on the book, this happened when I flipped it over. Should I not use masking tape for this?

I was considering pushing it to the edge of the table so I could flip the pegboard with the book that way but i think it would have moved the beads around too much.

I would do the normal tape method but when I do it with mini beads there’s always a good amount that don’t stick. I’m thinking I just need to change the tape but I’m not sure