Don't panic, my mum quietly freaked out when I told her I was pregnant with my first... just because she didn't think my relationship was going to last and she's one of those people who kind of clings to her kids because it makes her feel needed to have them around, and then when they do things like move out or whatever she gets upset because it means they don't need her so much anymore... it isn't just younger parents either, one of my friends was 27 when she found out she was having a baby and her parents hit the roof, didn't speak to her for months and just generally thought she was 'ruining her life' because she was 'too young' to be a mum...
My mum was also mortified that I was making her a grandmother before she turned 50, but as the pregnancy progressed and she could see that my DH and I were blissfully happy and coping very well together, she calmed down and got so excited you would have thought it was her baby on the way!!

I'm sure your parents will relax, they are probably just concerned because they are so far away and can't be at your side in a moment's notice if you need them, and it always makes people feel old to see their kids do things like leave school, get married, and of course have babies... kind of reminds them they're one step closer to the grave, really!!

Good luck with them, just try and casually explain that they shouldn't be worried about you because they did their job right, they've raised a sensible woman who is capable of making her own decisions and handling any curveballs life throws at you, and that you want them to be involved (but not TOO involved, obviously). Some parents feel left out of this kind of stuff, especially if they don't live nearby, and they might feel a bit miffed that they might 'miss out' on this amazing experience.
I'm sure they will get more and more excited for you as they get a bit more time to let things sink in, though, so please try not to worry too much, or get angry at them.