How do I erase my stuff off a locked MacBook

This may help.

1. Shut down your Mac, then start up from macOS recovery.
2. When you're asked to select an admin user you know the password for, choose Erase Mac from the Recovery Assistant menu in the menu bar.
3. From the Erase Mac window, click Erase Mac, then click Erase Mac to confirm. 
4. If your Mac restarts to a flashing question mark, press and hold the power button for a few seconds until your Mac turns off.
5. Start up from macOS Recovery again, then reinstall macOS. For details, see How to reinstall macOS. 

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Get started with your Mac – Apple Support (AU)

Hopefully this might help you a bit. Otherwise, you might be able to go into an Apple Store and have someone there help you get around your Mac 😉

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