tndisneyfan, a twelve digit confirmation number is what you should have. Just by way of trouble shooting - are you positive that this is the right day for your 90+10 to open up? According to the ADR calculator, September 19 (today) is the day you could do 90+10 for a 12/18 arrival.
If you put in your twelve digit number and the site just responds with a string of red numbers beginning with an E, that's indicating a problem with the system, not necessarily with your reservation. I got that message a few times when I was trying to do online ADRs, but eventually I got it to go away.