I don't think there is a right or wrong answer here. It is totally up to you. You can go and help without saying a word about it. Is that what you really want to do, though? You joined the autism awareness group, so you might find yourself wanting to speak out and move into a greater advocacy role. This still does not necessarily entail disclosing your diagnosis. What would be the cons of disclosing? What are you worried about?
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Great spirits have always encountered violent opposition from mediocre minds - Albert Einstein.