I took the inner pot to the mikveh and immersed it. However, a friend told me that I could not use it because it was given to me by a non-Jew. If this is true, what should I do?
What you did seems to be just fine, and It is hard to understand just what your friend meant. The halacha is that a utensil that was owned by a gentile and acquired by a Jew needs to be toveled before using it, which is exactly what you did.