Really getting worried about the group ride tomorrow

The one I want to do is 70 mi. I’m starting to get really nervous. The group is supposed to be 18-20 mph. I can do Oak mnt twice and average 18. I could do a pretty decent mostly flatish course back on campus at 19 no problem. 

But this one scares me.

I don’t want to get dropped, and not know how to get home. No one is at home to come get me if I get lost. I’m terrified of a flat because I still struggle sometimes with the CO2 cartridges.

A few teammates are doing it, but one is so super good I know she’ll be leading the pack. Another is a friend that I’ve hung with most of the summer, but he’s going to be riding with another of his friends. I don’t know what he’ll do if I do start falling behind. He might leave me, or he might leave his friend. It all depends on his mood tomorrow. 

I haven’t done a group ride since I started cycling way back last fall, and then I was dropped faster than you could say GO. :/ I’m faster now, but idk how fast everyone else is.

I’m so worried. 

I don’t know what to do about it either. 

I possibly could do the 40 mi route, one I know I could make an easy ride.

But…

I want to do the 70 mi one. 

:[

Tomorrow’s long ride info

What I normally do

http://www.mapmyride.com/routes/view/35705516

I can’t get it to load.

Anyway, I do that averaging right at 18.

Should I just go for it tomorrow?