Solution 1:

The NOAD reports that aren't is the contraction of are not, and am not; in the latter case, it is used only in questions.

Why aren't I being given a pay raise?

The Collins English Dictionary says the same, but it says that using aren't as contraction of am not is informal, and chiefly British.

  1. informal, mainly British (used in interrogative sentences)
    am not

Solution 2:

Aren't I? is standard English as the negative interrogative of I am. So it is correct.

Ain't I? is also common though regarded as a lower register. Am I not? sounds far too picky. I am, init? is also used, though I hate it. Amn't I might be logical, but only seems to exist, if at all, in Scottish or Irish dialect.