Thanks for the advice! I should point out the Wizard you fight is not a boss; there must've been some glitch because you missed the actual second boss fight!
I think a map is a good idea. I'm not sure about a minimap but perhaps maybe a map that you can open up with tab whenever that shows you where you have and haven't explored, because I notice a lot of people miss small routes they didn't notice on their first time through. Environmental detail may also solve this.
I'll upload a new version that fixes this and just for conveniences sake I'll also upload a version that skips you straight to the boss fight. Cheers!