I would suggest saving to the cloud rather than on the iPad. This will definitely free up space.
If you are saving to File on the iPad though, to make sure you're only working on one file, once you Export to psd, always reopen in either Fresco or Photosho from the same psd file. So rather than using the Recent list in Fresco go to Import and Open to navigate to where ever you have saved the psd file to.