J’ai très bien mangé, merci.
zhay TRAY BYAA mah-ZHAY, mair-SEE. Click below to hear.
No, thank you, I’ve had plenty/quite enough. No thanks, I’m stuffed/full.
Version one: polite company. Version two: casual company. Literally: I’ve eaten very well, thank you.
Note that you don’t have to say Non, merci. As you are saying the phrase above, you are giving your head a slight shake “no”, so the negative is implicit. When you have eaten enough, you may also cross your knife and fork on the plate, making an X. That’s the customary sign of having finished your meal.
Secondly, you do not answer the question directly. The question was, Will you have some more (potatoes, roast beef, salad…)? Vous reprendrez…? (voo ruh-prah-DRAY…?) or Encore…? The polite answer, if you don’t want any, is above. Nothing else. (There is no “proper” rude answer….) If you want more, you should say, Je veux bien, merci! (zhuh vuh beeYAA, mair-SEE.)
Under no circumstances should you believe the dictionary when you look up “full”. For a woman to say Je suis pleine (zhuh swee PLENN) is a vulgar way to say I am pregnant. For a man to say Je suis plein (zhuh swee PLAA, the masculine form) is just plain nonsense.
Please don’t make this very anglophone mistake! Save plein(e) for glasses, bowls, backpacks, boxes, and the like.