there is a scratch converter that you have to use, other wise it won't work
Viewing post in Can you use Scratch as an engine?
https://junebeetle.github.io/converter/ It took my a while to find it, but here you go!!
also, did you know that you can just make the game in scratch3 then convert it to a scratch2 file? https://github.com/RexScratch/sb3tosb2