If you've accidentally scanned the same document twice, or decide you want to try again after you've saved a scanned document, you can delete a single scan without having to delete an entire Note document.
- Tap your scanned document
- Tap the Trash Can in the bottom-right corner
- Tap Delete Scan.
This only deletes the specific scanned page you've selected. If you want to delete the entire document, simply delete the note.