I used actually in this sentence but my teacher said that doesn't make sense. He looks like fearless but actually he is not so brave. What did I do wrong?
There is something wrong with that sentence, but it's not the word "actually". To be grammatical, the first part should be something like: "he looks fearless but", "he looks like he is fearless but", or "he looks like a hero but".
In this construction, an adjective should go directly after "looks". You can put nouns or phrases after "he looks like".
In my mind, the "actually" sounds a little off where it's located.
I would say, "He looks fearless, but he is actually not so brave."
I think this may just be a matter of personal preference, as I don't see anything grammatically incorrect with either construction.