What should I do about my work permit and visa before leaving Thailand after my contract with Rajabhat university?

I have an unusual issue I'd appreciate some advice on. I signed for 3 months with a Rajabhat university. The contract expires Nov 30. I'm on a single non-B that expires Nov 26. I'm not interested in any more contracts with them and I've told them so in an email to their directors, even though I don't believe I have to give so much notice (or even any notice) for a 3 month contract which really amounts to a probation period. But I'm just trying to cover all my bases. The thing is, they never took me to the Labor office to get my work permit. I've been told that due to this oversight I'm not in the system as working in Thailand. Is there anything I need to get from the school before I leave the country or am I just good to go? Do I need local immigration to cancel my non-B? Thanks.