Even when the amount is much too much, we often use "a bit too much" to be more polite.
A: [brings B three scoops of ice cream] Here you are. Enjoy!
B: Ohhh, that a bit too much ice cream for me. Two scoops is even a bit too much. If it's not too much trouble, could you take back a scoop and a half?
A: Do you want a full glass of milk?
B: No, that's a bit too much for me. Please give me just three quarter's of a glass.