“is there some maintenance that I should be doing and missed?”
I don’t have the ability to consult a Honda Fit Owner’s Manual, but you do.
If you take a look at your manual and compare the Honda maintenance schedule contained therein with your maintenance receipts from the past two years, you will be able to tell whether you have maintained the car adequately.
That being said, it is possible that you have a broken motor mount, but I think it is more likely that skipped maintenance is to blame for this “vibration”.