Yeah, level 20 wont take any time to get back at all really. Id start over so the story can be fresher in your head and you can grow into your class(es) more organically. However if you do decide to stick it out, now that your control setup is how you want it you can always take some time to read spell, trait, and buff descriptions(i added this specifically because there are several classes with abilities that grant you a buff status without ever telling you what that status does) to figure out what your abilities do again and how you should use them. Follow that with a short session either with a training dummy or maybe a short session of fates or something to get a feel for how your class flows again. Then ask with any specific questions you dont find an answer for.