Hi mwietro,
Thank you for participating in the Apple Support Communities. We understand that Numbers keeps opening the same spreadsheet when you open the Numbers app on your iPad. You'll want to make sure you've properly closed the file. In order to close a document, tap the Spreadsheets link at the top-left of the page. This should save any changes that you have made and return you to the file browser. This article has some helpful information about this: Open a spreadsheet in Numbers on iPad.
"Open an existing spreadsheet in Numbers
- Open Numbers, and if a spreadsheet is already open, tap Spreadsheets in the top-left corner to see all your spreadsheets.
- Tap a thumbnail to open a spreadsheet.
If you don’t see the spreadsheet you want to open, try searching for it or tap the link in the top-left corner to browse Recents or a different location. See Find a spreadsheet in Numbers on iPad.
3. To make changes to the spreadsheet, you may need to tap edit at the top of the screen."
We hope this helps.
Take care.