Turning styles off did the trick. Course, now even the styles portion I liked is off. I tried editing the book in Sigil, in my Calibre Library directory -- edited the styles in the ebook. But it didn't seem to "take". I'm a developer, so changing a stylesheet isn't something new to me.
I set the bottom and top margins to 0, and still I can't seem to remove that "double spacing" issue.
Turning off styles will work for now, but I'd like to just fix the styles.