Ok cool
You also seem certain that the url and paths match up, but just to rule it out, Can you copypaste the url from your webrowser and the exact path from the root of you mac? (right click hold alt and then choose copy as pathname)
Also, in your MAMP settings, which folder is set as your root for the websites? Also copypaste exact path here.
Which exact error are you getting?
Whats really helpful is a screenshot of the full screen when the error shows.