No need to be nervous man. It's fairly common. If you have some reservations maybe ask a trusted friend or family member if you can have them shipped to their house. If you pay with a credit card, you are still going to need to provide your personal info anyway. A lot of places still accept money orders if you don't mind waiting the extra 7-10 days until they receive it. I would recommend doing that for a little extra piece of mind if you are still concerned. Just make sure you use the pink international ones from the Post Office.
Hemp Depot carries a lot of popular strains and ship from Canada.
In all honesty though man, if you are freaking out about ordering seeds, how are you going to feel when you have actually plants in your house?