personally I think you should tell them , about having autism ..just so they can know and you can be yourself around them .Trust me not everyone is ignorant and soon they will even forget that you mentioned that you were autistic... I have seen it happen with my friend she had Bipolar disorder , and she did tell everyone, but it didn't affect how people saw her ,she was never stigmatized. you might as well get it over and done with ...but it is your choice , and if you decide not to am sure they would never know you have autism. I hope this helps