Really difficult decision

Ok so I'm 18 and about to graduate high school, I am already signed up for college and I am signed up for my classes but I keep thinking and I don't feel like that is what I am called to do. I just keep thinking of this missionary organization that has recently started partnering with my church, and my family is hosting one of the girls, and it sounds exactly like what I've always wanted to do, which is travel, meet new people, see new things, and help make a positive impact on others while I do it, and grow in my faith, but I'm already signed up for school, and it feels like what I feel called to do, but I'm not sure what I am going to do because I don't want to disappoint my family if I don't go to college right away. Plus I don't know if my mom could handle me going very far, because she freaked out when my sister moved to a different part of the state, and I've always been hers and my dads emotional support and the only one who can handle stressful situations, and I really could use some advice if possible.