Oil Change Help - Rookie

[DrCactus]

Hey guys I did my first ever oil change myself last week and I noticed today that I have oil drips on the ground. I replaced the drain plug with a new one and also a new crush ring. However, I remember I saw some little rubber like ring in the old oil but then forgot about it.... I am wondering if it was some kind of gasket which is required long with the crush ring or something???? Would oil leak if I over filled the car with oil or something.... any ideas would be helpful... I have to get under the car this weekend to check to see where the oil is coming from. Could be possible I over tightened it? I just tightened it by hand - maybe not tight enough ?

Thanks!