You can't know it's fixed unless you buy a copy (you'll get your royalty) and look at it in a dedicated e-reader (Nook, for example) or at least an app (Nook for PC, for example).
I think there are two lessons to be learned from your experience. The first is not to use Scrivener to create an e-book. I would output that Scrivener file to epub, then open the epub in Sigil and fix it there. Use Sigil's validator, called Flight Crew, which now must be added as a plug-in. That will keep you from making major mistakes as you go along. Then, before publishing, pass it through EpubCheck at
http://validator.idpf.org/
The second lesson seems to be: don't use Smashwords to convert your book. I gave up on SW some years ago in favor of distributing directly to Barnes & Noble, Apple, and Kobo; now I use Draft2Digital as my aggregator.
There's a learning curve to everything. Just as you set out to learn to write, now set out to learn a bit about html and css and Sigil. Then your books won't come back to bite you. I have a fairly simple-minded book about all this, which you can find by plugging
Notjohn into the search engine at Amazon, Barnes & Noble, Kobo, Google Play, and just about everyone else except Apple, which objects to the many references to its competitors. I recommend the book (but then I would, wouldn't I?).