Hi Michael,
welcome to the forum!
Hmmm... There are so many ways to play "badly", I don't know where to even start...
One can play too loudly. One can play too quietly. One can play with unsteady tempo. One can play with timing that's almost, but not quite, correct. One can play with poor pronunciation (no clear distinction between bass, tone, and slap). One can play an accompaniment part that doesn't belong with the rhythm that's being played. One can play solos that clash with the dundun melody. One can play technically well, and still play badly because the musicality isn't there.
So, plenty of ways to do it wrong

My suggestion would be that, if you are serious about the djembe, to take some lessons with a good teacher to get an idea of what this music is all about. I have to warn you though: it's a journey of many years, and a highly addictive one for some people

Another idea is to see whether you can find a drum circle or two in your area and go along to have a listen (and a play!). Just by being around and observing, you will get an idea of what works and what not.
Other than that, don't worry too much about how you play. Instead, just enjoy the experience and have fun. Chances are that, if you are having fun, you won't play badly, no matter what your skill level.
Cheers,
Michi.