Fitness
Most peoples' biggest concern in joining a cycling club is whether they can keep up. Having nurtured many newcomers to Essex CTC over the years we know that it may take several months before you feel confident. During that time we would encourage you to ride to point no further than elevenses. Some sections organise short rides specifically for newcomers. You might also try riding a short local route to help improve fitness.
Make the effort because it's worth it. If you're convinced then contact your local section Secretary will introduce you to the group. If you keep riding for 6 months then your fitness and stamina will steadily improve - that's a promise!