Purchase amount wrong

So today me and my friend went to mugg and bean riverside in vanderbijlpark. Our bill was R157. We both paid with our cards. She paid R90 and I paid R90. We told the waiter to place R90 on each card. Trusting the service I did not dubble check seeing that we both said R90. So as I was reading my SMS tonight I saw a R180 from Mugg and Bean. The waiter typed in R180. Yes I am also to blame I should have checked but hell there is a BIG difference between R90 and R180.