I'm completely full.
我吃撑了！
completely 彻底地；完全地。彻底吃饱了，吃撑了呀！
I am stuffed.
我吃撑了。
stuffed 塞满的；填满的。
I’ve had too much already.
我已经吃太多了。
I have had more than enough already.
我今天吃太多了。
I can’t eat another bite.
我一口也吃不下了。
I can hardly move.
我已经撑得动不了了。
I'll burst if I eat another mouthful.
再吃一口我肚子就要爆了。