It's not the worse lie.... and honestly if you were young when you made it up people won't be hurt or anything like that it's the literal definition of a white lie...... I dated a guy in high school and over a year in he randomly one day told me that when he was 6 he lied and convinced the doctors he couldn't see right and they gave him glasses (which made him strain at first then he could see) and the dummy permanently needs glasses now all because he thought they were cool as a kid !! Our entire friend group thought it was hilarious! So I would be to worried about it! If they are real friends they will 100% just laugh at how silly it is and move on