Your teacher is correct. "just enough food" is natural. "just enough amount of food" is incorrect. "a sufficient amount of food" is correct but rather formal.

It looks like you want to describe the amount of food. The word 'enough' does that by itself since it refers to quantity - enough food, enough time, enough space - we understand that you mean that the amount was enough. Its the same reason we wouldn't say something like 'we went gone to the shop' since went means that you had gone. I think the reason you might be confused is that we would use amount if you were to say something like 'the right amount of food', 'a decent amount of food' or 'a good amount of food'. The difference is that 'right', 'decent' and 'good' all have separate meanings other than quantity and just saying 'the right food', 'decent food' and 'good food' doesn't imply anything about the quantity of food.

I'm going to post this as an "answer" so that other English speakers can comment. 소영 ask: "Thx, but could you explain why it is incorrect? To me, "enough amount" seems to make sense." It's difficult! I don't know if I can! I'm making up an explanation. I hope it's right. What do other English speakers think? It seems to me that the only thing that can follow the phrase "I enough" is either a plural noun or an uncountable noun. I have enough nails, I have enough friends, I have enough money, I have enough gasoline. I can't say "I have enough keyboard," "I have enough ring," "I have enough telephone." The word "amount" is singular. "Enough amount" just sounds wrong. But I'm unhappy with my own answer, because we can say "I have a large enough amount of food," and I don't know why the word "large" changes anything.

In Chinese, it makes sense.

Your teacher was right about correcting you. However, you can use them together: The amount of food that we had was just enough to feed everyone.