Looking to build a better sign-up form

Hello,

I'm building a sign-up form template for 1-on-1 Q&A sessions (20-minutes each throughout an entire day) that have limited capacity, and I don't want folks with flexible morals to be able to overwrite someone else's claim to a particular spot.

Is there a way to setup text boxes so that once someone enters information (name) into the box that it their particular selected text box is no longer able to be edited?

Thanks!
Seth