How do I approach girls in groups?

I'm a 14 year old boy from Norway, now I'm at vacation in USA. I'll be here for 3 weeks and I'm only with my parents, so want to make some friends (girls). And my problem is my approach anxiety, It's real hard for me to go up to a girl or a group of girls and start talking. And I also have no idea what to say. Today I was at this fast food place, when I was done eating I saw two girls sitting at a table and I grew some balls and walked over. I only asked what time it was, but still that was a huge step for me. But I really want to get to know girls, but they are always in groups and it seems like their in another world also, so I feel like it would be bothering them if I approached. So I'm really stuck here, so I would like help. And I've heard americans are really nice, and it seemed like the two girls I talked to where also. But I always feel like they will reject me, so please help me out.