Is the money I took from philanthropists, which exceeded the cost of my father's surgery, lawful or unlawful?

If the donor is informed of the true situation, and that the amount exceeds the cost of the operation, then there is no harm in taking ownership of it. However, if the entire amount is requested under the pretense that it is the cost of the operation, then this involves deception, and the excess amount must be returned to the donor. Asking people for money is permissible only in specific cases or out of necessity.