Sadly that's where I stand in this as well, but I think you couldn't use RND like we are right now, we would need a controlled RND, like a RND under certain conditions and based on the conditions it would randomly generate under those circumstances. And to do that there would have to be lots of math and loops.
So I tried it and yeah! It works, but I'll have to add a couple of things, like rules so it's not so all over the place and looks more like terrain and tree generation!
I think you want to press a button and go to a loop, right?
Use IF BUTTON(2) AND #A THEN GOTO @LOOP. I don't see why you saving whatever text the player puts in INPUT into YES$, I think your trying to have the player input "Yes" to have the game started, to that you'll have to use INPUT "Play" ; VARIABLE$
IF VARIABLE$=="Yes" THEN GOTO @LOOP