Don't let the photographer forget a picture of the bride and groom!! Yes, this happened to us. We laugh about it now, and we eventually got one made by somehow taking my grandma out of a picture, taking my DH from another and adding him to the grandma's spot. Our photographer had ordered his digital camera but didn't have it yet, so this was all on film, and it was very expensive for the photographer. It was partially my fault, we were getting ready to take it, and I noticed my flower girl leaning on the steps watching us, and it was adorable. I motioned for him to get a picture of her watching, DH stepped away, and that is one of my favorite pictures from our wedding to this day. We got distracted by that and never did get the pic of the two of us by ourselves.
Try not to stress over little things. *Something* will probably go wrong, hopefully something small, but chances are, no one but you and your DH or whoever helped you with planning will know.
Take a few minutes sometime during the day, look around, soak it all in, and enjoy yourself.