Thank you card etiquette

Hi everyone, I have been reading everything on this site for months, but never posted. I just wanted to thank everyone for all of the great advise!

My question: I just got my thank you cards back from the printer and now I'm questioning something. On the outside flap, I have Mr. and Mrs...and now, I'm wondering if I should've just put our first names instead. What did all of you do?

P.S. They made an error on a few things, so if I want to change this, I probably still have the option.

That is proper etiquette
This is a posting board and I am only warning brides because there is enough stress planning a wedding that you do not need more. You may take this information however you would like, the fact is that my experiences with ADRIENNE'S BRIDAL SHOP were HORRIBLE!!!!