Ah I see, that makes sense.
I'm not sure if this is a good suggestion, but you could require stars to 100% a level, it incentivizes the player to "use the whole map" in a single run. You would probably have to remove the hidden stars from the game if you did this as it would be frustrating to complete if you couldn't find the last star. Downside is that there is some amount of backtracking, I'm not sure whether the positives outweigh the negatives.