For your first group ride, tell the group it is your first ride and ask if you can sit in for a while to see what happens. Then, when your confidence is there, try and roll a couple of turns. Others will give you advice and let you know what you need to do - and not do.
Definitely, do NOT try and venture outside your capacity, as that is the time that you may make a mistake, touch a wheel, or something else and end up crashing. If it gets too hard - sit at the back, or drop out, to avoid a mishap.
It is a bit intimidating at first, but once you're in the groove, pacelines are a LOT of fun - the hum of the tyres, gears and carbon rims in a bunch is fantastic!
cheers