The fear and anxiety are totally normal. I found out we were having twins and DH wasn't with me for the appointment. I called him, asked him if he was sitting down...then broke the news. He was over the moon, I was petrified for a while.
Now that our boys are 2.5 (I have no idea how all that time passed so quickly!)...and even when we first brought them home, I have felt so blessed to have two of them and I can't imagine it any other way. It helped that they were our first and will be our only children.
You'll get a lot of advice as you go through your pregnancy - I can say that schedules and being pretty strict about keeping to them are our saviours.
When you get closer to your due date - say 'yes' to anyone who offers to help, and be specific about what you need - I had friends who would just swing by our house and run a load of laundry, just to help out and it meant SO much to me - every little thing helps.
Talking to twin moms definitely helps a ton too.
Best wishes to everyone for long and healthy multiples pregnancies.