Can't Decide

I can't make up my mind about what to do next week. I'm really stuck. Here are the 2 things I'm trying to decide between:
My stake does this thing called "Called to Serve", where the youth 16-18 can go on a mini mission. We travel with missionaries from the local mission area, our mission area that we're in is the Peoria, IL mission. So youth travel around the local area to whever some fairly nearby missionaries are at. Last year I went with sister missionaries from Bettendorf and I enjoyed every moment of it, it was so much fun, such a rewarding experience. There are also sister missionaries farther off in places like Cartheridge, IL (where Cartheridge Jail is), and Peoria, IL. I'd really like to be able to go father off and out of my own stake area. Oh, and it lasts from Thursday afternoon-Sunday evening. It's 3 full days of being a missionary.
The problem is, this mini mission falls on the same weekend that my dad has off of work.
My family has been planning a day trip to America's Largest Water Park - Noah's Ark Water Park. We take this trip at least once a year. It's always a ton of fun, I'm such a sucker for thrill rides. Absolutely love them. Plus, it's time to spend with the family, which may not get to happen as often, now that 2 of us 5 kids are now in college. But we might possibly go again in August when my aunt comes to town from California, and this time we'd spend 2 days there, one at Noah's Ark and the other at Mt. Olympus, a theme park down the street that has some fun roller coasters, but the main attraction (for our family at least) is the amazing moster wave pool. Its waves aren't like your average wave pool, where they're kind of everywhere and just make you sea sick. No, these are huge 12 ft waves that happen once every 90 seconds and slam down and it's just sooooo much, we usually spend the morning doing roller coasters, eat lunch, and spend the rest of the day from 1-6 just at the wave pool, it never gets boring.
However, we wouldn't be going there on the one day trip next week, we'd just be going to Noah's Ark, which is still a lot of fun.
I just can't make up my mind! I know there will be other times when we can go out as a family to Noah's Ark, but I won't get to be able to go on this missionary thing again. I probably won't be able to serve a full time mission anyway because of my health restrictions. I want to do this now! But I don't want to miss fun times with my family, either.

So which one? Doing the Lord's service, or spending time with Family, the ultimate focus of life? My parents would like for me to come with them, they say if I don't come it will really feel like something is missing, and I'd hate to have that guilt with me while doing the mission. On the other hand, I'd really hate it if I didn't go on the mini mission, the weather ended up being crappy, and we didn't go to the water park after all. But even if we do go and it's a great day, I'll still be really upset that I couldn't go on the mission. I've been looking forward to it since last year when I came home from the first one!

Probably getting too in depth into it, but I like to appreciate everything I do, and this is a tough one.
Any input? Any at all? Auuugghhh this is so difficult!!