OP, don't feel ashamed. You said that you rode with the A group without realising it. Awesome. There is nothing wrong with getting dropped. There is nothing wrong with bonking. There only is a problem when you do it repeatedly Without Learning from it. In the future, make sure you are well fueled, and if you're going to push it, make sure that you have a backup plan in case something goes wrong. Last, did you have fun? If the experience wasn't fun (type 2 fun (fun in retrospect)), then something is wrong.
"Get busy living, or get busy dying."
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Somewhere, a village is missing its idiot.