General relativity is a theory of gravity.
General Relativity is a Theory that INCLUDES gravity. It attempts to explain gravity in a larger context. The smaller issue of how gravity works is a Law.
GR has been well-confirmed for several decades now and is generally believed to be true- but that is not long enough to promote it to a law. For example a geocentric model of the universe was confirmed by every prediction and observation for 1400 years- but it was wrong. It turned out another model, the heliocentric model, also explained the data.