I ride in the big in the big chain ring when I need to... I don't avoid any particular gear. If for some reason my legs are achy and barking at me, I use a easier gear... If I want to test myself and sprint a little... I grab that extra gear and GO for it. They're isn't a right or wrong.

Good luck and keep with it!
Shannon

Ps. You didn't happen to mention what types of bikes the others in the C group were riding. A roadie with thinner tires is going to go faster then your FX at the same level of effort. Not that there is anything wrong with your bike, but you will work harder to match speeds, so take it easy on yourself and don't be afraid to use that big chain ring!