Authenticity is ones degree to which you are true to your own personality despite external pressures.
If I asked you right now if you are authentic every single time of your life, chances are you will tell me something in the lines of ”but of course I am!”. And in your case it might well be.
More often than not we give in to the social pressure and are what we are expected to be by others. When we meet people who are authentic there is this sense of completeness about them, they somehow seem to be more real than the rest of us.
For one day, one day only try to be who you really are.
And when that day is over, write about your experience as yourself ™