I want to schedule an appointment at the store to make sure my computer is wiped

You can try but the genius bar addresses hardware issues. Here are Apple's instructions

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

If you want to try for an appointment, go ahead - we are other users and do not make appointments for you.

If you did step 7. in the proper procedure, you did this and the Mac should be ready to begin renewed operation:

7. Reinstall macOS

1. While still in macOS Recovery, choose Reinstall macOS, then follow the onscreen instructions. Learn more about reinstalling macOS from macOS Recovery. 
2. After reinstalling macOS, your Mac restarts to a setup assistant. Press Command-Q to shut down instead of continuing setup.

If you didn't do the proper procedure, babowa offers it for you to follow if you choose.