This reads like a joke question, I know, but I actually mean it.
Are you supposed to answer this sort of suggestive question with honesty? Or is this generally meant to be answered in coy and or affirmation? Because I don’t want to ruin the mood but I also don’t want to unwittingly spoil her expectations. (FYI, I’m average sized.)
You’re not supposed to be insecure about it.
You can be honest , you can joke about it. I’d probably just tell them it’s so boringly average, I measure every day and compare to the wikipedia article on penis size.