I have messed up my rights on a list, so I can still view it, but cannot edit it. I need full permissions on it again.
Is there a way to set my admin account back to full rights via powershell?
Sounds like a sledgehammer to crack a nut. Do you have anybody with Site Collection Admin permissions that can reset them for you? In fact, if you have access to run PowerShell then you can almost certainly make yourself a Site Collection Admin.