I have to check on some medical bills I might not have entered. Could I return in a week or so to complete this return, or do I have to start over when I do return?

Yes, you can just come back when you have the information you need and pick up right where you left off. Just remember to sign in with the same User ID as you used to start your return, then choose, take me to my return, and it will ask you if you would like to pick up right where you left off.