Catherine, its okay to freak out. I just thought about it the other day, wow I am married, the wedding I dreamed of my whole life is over, no re-dos, I am someones wife and its all a very scary process, but think about the life you have built together, your son and all the years you have spent together. Getting married is what you have wanted so now you just have to decide how to express that love for each other.
I think its such a cute thing for him to tell you to pick a number, very creative and unique. He obviously loves you and knows that you have been a very patient woman. You should be excited for this, don't get down on yourself.
Start planning woman!!!