My first ride w/my new bike was an organized ride, I was still on platform pedals and didn't even know enough to be scared! It turned out all OK.

My advice would be to maybe stick w/platform pedals until you are more comfortable overall w/your bike, shifting, stopping, getting on and off, all that. Maybe just use the cycling shoes w/the platform pedals to give you more power and more comfort in your feet.

Stick to the back of the pack, ride w/a pal.

That's a challenging distance for only riding a short time, but I'm sure you can do it w/style and aplomb!

Most important, have fun, lots of fun.

Colleen