I have a continued part-time internship with a company I'm about to renege on. What do I do?

I know this is a terrible situation, but I was able to find a full-time offer that pays 2.5x the first-year comp (going from sell-side to prop firm) and the firm I accepted the offer with in September allowed me to continue part-time to finish my studies. I am also currently working in the Spring and the money has been able to allow me to finish college debt-free. Should I wait until my Spring Internship finishes to renege on the full-time? I feel like that's the best course of action is to accept FTO at the prop and renege on the other offer after I finish the part-time internship in the Spring.