5 % keyword density would be a little higher than I'd like, but don't worry too much about these numbers. Honestly just focus on if it reads humanly or not.
In briefly glancing at your site, I gotta admit that the links on the right to the articles seemed stuffed to me and I didn't much love the way it read. I understand that each article is about "fake diplomas" (!! I didn't even know this was a thing, WEIRD!) but there's gotta be a better way to title the articles. It is quite clear what you guys do and not necessary to repeat that in the article's title. Your domain is fake diploma.com... that does it right there. Call an article "How to Frame Your Masterpiece" or something instead. Make it fun, funny, and spice it up a bit.
Otherwise don't worry too much about this recommendation in Moz Pro. A lot of these things are simply that, recommendations but not necessities. You may skate by just fine without changing a thing. That said, it's probably indicative of a usability issue that needs addressing and I think you might be surprised at the success you can gain by re-wording things a bit differently.
Like I said, don't worry about stuffing your main keyword in each of the titles. Everyone is going to know that you make fake diplomas.
Good luck!