When you open a project in On-Screen TakeOff, it is locked to prevent anyone else - or you in another session - from accessing it. If TakeOff is not closed down properly, then the lock will not be removed.
This will clear itself after 10 minutes. (opening before will reset the 10 min).
If you have not had TakeOff close improperly, and it says that you are the one with the project locked, then it's possible that it is running on another machine, for example an RDS server.
Check the project is not open elsewhere, if not wait for 10 mins or more before trying to open the project again.
Note: Support does not remove these locks.