(Question) How do you masterize your sets?

Make a new set? You could do all kinds of tricks masking errors but maybe that’s not an accurate way showing your techniques. Anyway, not knowing your problem, let’s say it’s a beat matching problem, take the outro part and filter it out, with some effects, reverb washes or whatever and suddenly remove it all and bring in the next entry when it’s playing alone. Any DAW or decent audio tool should have the means to do this.

FL Studio should work just fine. Audacity, too. I’m using Logic/Ableton Live myself but most modern audio tools should be fine.