Relax! You have met the leader and you have been honest about your experience level. It sounds like a wonderful way to be introduced into group riding. When I started I had no idea about gearing or anything else. Some very patient people rode with me and taught me so much. Group rides vary in purpose, speed, distance, etc. I now ride with a group 4 of my 5 riding days. It takes time to be comfortable but I went from being scared to ride behind someone and only able to ride 10 -15 miles to holding my own in a paceline for rides going 70+ miles. Let us know how it goes!