Unfortunately, as Communism has taught us, free things are not unlimited things. That being said, an easy solution to your grievance is to make multiple parts. I use this in my own creation, and it is fine. In fact, it’s often pretty advantageous as you can copy certain rooms onto the new part without having to recreate it and it saves space.
RPG Playground can only hold so much, as if you’ve placed a hundred actors in a scene you’ll see. But it’s free and easy. You can’t expect everything for nothing, but there are ways to get around it; be creative.