Not exactly sure how, but I managed to get stuck small with no enemies around right over the red star. It involved shelless koopas that I somehow stomped while getting hit. Sad times. I'd ad some munchers there.
I'd maybe make it so the edge of the level is NOT the edge of the screen, so that your item box will follow you even on the far edge. I'd just adjust the level boundary well beyond the physical walls of the level.