do you tell your table there’s an autograt?

i feel so bad. my store just started auto gratuity on large parties. it was a 260$ bill and the auto grat brought it to 300. it says on the bottom of the receipt, but they still tipped an extra 20%. i feel awful, but all of my coworkers were cheering me on. it was electronic and automatic; i didn’t input it. i even asked my manager if they could reverse it and she said it would take days and it’s not worth it. the table has no idea, and i feel like this is a win in most servers eyes.. i just feel like i robbed them