Just ride with this group more and you will get stronger. The others in the group have probably been doing a lot more climbing than you. Also, club riders often slack off somewhat on the flats, then push themselves to the max on the climbs. Try to save your energy on the easy parts of the ride, so you have something extra to keep up on the climbs.

While you're still improving, try to remember the faces of the slower climbers and you can always ride with them when you get dropped. Don't try to keep up with the faster riders unless you don't mind getting dropped regularly.