Well, I got my first "gig" as some people might call it. I get to play Every Rose Has It's Thorn at our schools biggest band/vocal concert. There's only one problem...

I can't play rythm guitar and sing at the same time! When I try to do it, I tend to make the rythm guitar's rythm the same as the vocals and when I try to do otherwise, I screw up...majorly.

So, should I just let myself do this or should I practice the chord progression and then put the words on top?

P.S. This concert is the 31st. I know the lyrics, chords, etc. and I'm planning to skip the solo because I would be a one man band.
it takes time to get used to singing and playing at the same time, especially when the singing doesn't line up with the rythm of the guitar.

I technically have the ability to sing and play at the same time, but nobody really wants to listen to my singing

Here is a good way to start practicing. find a few words that line up with some of the major strumming points (like at the end of a phrase). Focus on your singing and try to hit those specific words at the same time as their corresponding strums. As you get better at this, the rest of they lyrics will come naturally and fall into place.