Hi casmic!
Congratulations on making the huge step of scheduling an appointment!

Even though you are probably terrified of the next step, you should be very proud of yourself for picking up the phone and making the appointment. Sometimes I think just getting the ball rolling is the hardest part.
There's not much any of us can say to take away the anxiety, other than to assure you that the first visit should just involve the dentist having a look around your mouth visually, and probably some x-rays. And, your dentist will likely be very professional and compassionate, and won't lecture or belittle you. On my first visit back, I was certain that the dentist would shriek in horror at the state of my teeth, or at the very least recoil in disgust before composing herself. Instead she was very gentle and kind and acted like she sees broken, decaying teeth all the time. (Actually, most dentists do...) I almost burst into tears about how comforting and kind everyone was.
Your anxiety is perfectly normal, at least among fellow phobics. Unfortunately, you're going to have to work up the courage to get past the anxiety and get into the chair, but once you get there you'll find that the worrying was the worst part. Don't feel ashamed for being afraid when others seem to have such an easy time of going to the dentist. Dental phobia is a real thing and the response from your body is just as real as for any other "real" threat. It doesn't make you a wimp or a baby, it just means you have to fight extra hard against a runaway mind. We're all there with you! For us, no visit to the dentist (sometimes no
mention of a dentist) is small enough to count as "not a big deal."
I'll second toucan's suggestion:
On the actual morning, I got through the time by just concentrating very hard on each step I took towards going. Soak in the bath, find clothes etc. It's almost a relief when it's actually time to go! The waiting is over!
On my "big day", I had to talk myself through each tiny step-- lace up your left shoe, now lace up your right shoe, now stand up... but it kept my mind off You Know What, and kept me from turning tail at the last minute.
Hang in there! A week from now you'll be strutting out of the dentist's office, proud of yourself for surviving and excited to stop all the worrying. In the meantime, feel free to spew, vent, worry, ask questions, describe fears, or whatever here on the forum, and we'll try to keep your worries at bay.
Congrats again, and good luck!