(If you're even reading this) There is a dedicated red "contains" block in the variables category that scans your list verbatim for a matching element. This way you don't have to work with the way the green "contains" block retrieves information in a list.

However the real issue in your code is the "stop script" block, and the way it's functioning in your code (if the prior red "contains" block was implemented) is it halts the script every time the "if" loop is fulfilled. This looks like checking the list if it contains your newly selected number, which it won't upon initiation, fulfilling the "if" loop, then adding the number to the list and swapping the backdrop and immediately stopping the script. Obviously you want it to run repeatedly, so I'd say you replace the forever loop with a 27 loop and get rid of the stop block.