It took a dare at a trip to Disneyworld to get me to just try the kiddie coaster there!
I'd finally reached a point where I decided I needed to conquer a fear when I turned 30 years old. And since my research had shown that roller coasters are statistically safer than just about any mode of transport you can imagine (seriously, most accidents on coasters are due to riders neglecting to follow the written safety instructions before you board the ride!), I was able to talk myself into trying out a coaster, if only once to finally address that life long fear.
When you're ready to try to conquer that fear, you'll know. If you're not yet ready, there's absolutely nothing wrong or disappointing in that. If you truly do want to want to work towards conquering this fear, spend some free time researching about coasters first. Read about the various safety features, how they work, etc., so if anything you'll at least have peace of mind when your friends ride them. Honestly, doing this helped me the most in working towards addressing my fear of coasters. A good starting point is
http://www.rcdb.com/ (Roller Coaster DataBase). It details almost every coaster in the world and there are some links to sites that provide more info on coasters as well.
To be fair, Camp Snoopy really only has one mild coaster I'd recommend a neophyte to try - Lil Shaver, which is a powered coaster and doesn't have a high lift hill like the other two have. But even then, a lot of powered style coasters tend to ride rough (don't know why) so you may not get a ride that inspires you to try out other coasters!
And if it's any consolation, I spent the entire trip from the station and up the lift hill on my first "real" wooden roller coaster contemplating how to get the fu*% out of that restraint and out of the train! I was panicked by the time we hit the top, and it didn't help that my husband threw us on the Georgia Cyclone for my very first real coaster ride! Not smart thinkin' on the DH's part! That first drop (always the scariest part of any coaster) looked like it was completely vertical from 90 feet up. I proceeded to curse my husband out for the rest of the ride while holding on for dear life to the bar in front of me, much to the great amusement of the gentleman in the seat in front of us. ;)
But after it was over and I'd caught my breath, I realized it was amazing, scary, intense, and somehow still fun! Now, I was only able to ride two other coasters that day (adrenaline was pumping too high!) but I became hooked! To this day, roller coasters are like therapy for me... I get a lot of stress out while laughing and shouting on them.
I've been where you are and there nothing wrong with not enjoying or being able to handle coasters! My mom can't handle anything worse than a carousel (she also gets car sick easily) and a long time friend of mine can't stand the intense sensations coasters can produce either. Every person is different and if coasters aren't your cup of tea, then c'est la vie... Just tell your friends you enjoy watching them have fun on the coasters and take pics or videos of them as they ride! It'll be something you can all enjoy after the park trip too!