It has never been "over 50" but it has not always been "50." We started off with only 13, remember?
Perhaps you recall that it used to be 48, and then after Alaska and Hawaii became states, we had 50, and Hawaii and Alaska did not become states until 1959. Before that, we had nearly 50 years of having only 48 states, as Arizona was the last state of the contiguous United States to become the 48th state on February 14, 1912. So for that 47 year stretch we only had 48 states. But we've never had more than 50. Hawaii was the last state, which gained statehood on August 21, 1959. Alaska became a state earlier that year on January 3, 1959.