Others have made suggestions for programs designed to be more fully featured typesetting and layout options if that’s what you need…
…but I do want to push back at the idea that Scriv produces “unprofessional” outputs.
Sure, if you’re doing online magazine layouts, InDesign is a great option, but if you’re doing regular novel outputs you may actually find a lot of those little flourishes you’re planning to put in your epub actually make you look like vanity self-publishing.
The equivalent in printed paperbacks are the “fancy” font choices that are actually harder to read and the shockingly white paper pages that stand out hideously against the unbleached stock that actual publishers use.
All those “fancy” adornments in the text tend to be reserved for the expensive cloth bound hardcover collector versions of classics. On mass market ebooks… they’re awkward and intrusive. Scrivener will very comfortably produce an epub file that will look at home on your kindle next to anything on the actual professionally published shelves.
The epub and pdf linked in the first post on the thread linked here, for example, were produced entirely on Scrivener in about 2 minutes while highly sleep deprived: The Lippincott Dinner [aka - Villa Diodati 2]
So sure, buy your expensive magazine layout programs and tinker to your heart’s content, but you may not be being as “professional” as you think you are.