to be fair, £3.60 difference from £180ish isn't too bad.
Done some sums:
Original total pot: £186.24
Pot 1: £128
Actual Pot 1: £128 (assumed correct)
Error1: £0
Pot 2: £62
Actual Pot 2: £58.24
Error2: £3.76
combinedError = 3.76/186.24 * 100 = 2.02%
Error2perPerson = 3.76/(74+31) = 3.58p
Can everyone pay me 4 pence please?