Presumably you have, in place, an employment agreement and an Intellectual Property agreement. You should review them and, if necessary, discuss the situation

Presumably you have, in place, an employment agreement and an Intellectual Property agreement. You should review them and, if necessary, discuss the situation with a lawyer who is experienced in this sort of thing. You also need to know what your employer's intention is. If your "home-made project" was not excluded in your employment/IP agreement they may feel they already own the product.