Take a deep breath and let that anxiety go. The prep is the hardest unless you really like sitting on the toilet.
It sounds like your husband had one done so you know about the prep. I bought a couple of new magazines and gathered any needed supplies so I could camp out in the bathroom. I also gave myself a pedicure to keep busy.
The colonoscopy itself is the easiest because you don't remember anything. I remember them starting the meds and then magic--I was back in the little room with my husband. I've had two done and they have pretty much been the same.
What to do between now and Wednesday? Keep busy. When a negative, anxiety thought comes into your head--tell it "get out, I'm going to be fine" Then quickly find something that occupies your mind--talking to someone, getting busy on a project at work, playing a game on the computer--anything that requires your concentration.
Hang in there, we're here for you.