Is this my intellectual property legally?

So I modified a version of OS Ticket, a PHP based ticketing system, for my company. Previously, our company used Quickbooks Online and used the 'estimate' feature as their inventory of systems. THis was horrible so on my own time at home, I slowly modified and made a new ticketing system. I started using it for myself to manage repairs better and it worked great. The manager caught notice of the system and suggested we used it to replace the current system. At the time, I programmed EVERYTHING at home in my spare time. I was not given any company time to work on this. I was an hourly employee what the system got implemented. Three months later I was promoted to a salary position(basically made me the 'Network Admin + Lead Tech'). They would give me input on problems here and there and I would write fixes for them. I did this a few times for them. Fast forward another 6 months, and I am ready to leave this company. The system I made is our primary and only system in place now and I believe it is my property. I realize the database information belongs to them and that is not what I want. I want to just prevent them from further use once I do leave. Any input would be appreciated.