Your impression that the Titanic had two sister ships, Olympic and Britannic was correct.

The Olympic was scrapped in 1935, as one of your previous respondents has explained. The Britannic was not completed until the First World War. She was used as a hospital ship and torpedoed by a submarine in the Mediterranean in 1916.

None of the White Star liners survive but the tender Nomadic that they used to transfer passengers between ship and shore at Cherbourg has recently been purchased for preservation in Northern Ireland (where the White Star line ships were built at Belfast)

The ship you saw was the United States. She was the United States Line flagship, built with a lot of Government subsidy so that she could transport troops in wartime. She was incredibly fast - her speed was for many years a US state secret - and as a result she easily held the Blue Riband as the fastest passenger liner to cross the Atlantic. The United States was withdrawn in 1969 and subsequently got moved around to odd places, including Turkey.

I cannot imagine anybody in the United States (I am British) wanting to scrap such an iconic ship. The trouble is that preserved ships are very expensive to restore and maintain. Also, it appears that the United States has lost her fittings,which were notoriously all metal: her designer Gibbs allowed no wood anywhere, except the grand piano, ostensibly for fire reasons. This would make it difficult to show the ship in a historic shape: the Queen Mary was sailed to Long Beach immediately she was withdrawn from service and therefore her furniture etc. were still extant. So it is not surprising you are stuck with an eyesore.

P. S. I notice a previous respondent has suggested the ship you saw was the America. The United States ran in service along with a smaller, pre-Second World War ship called S.S. America, which I presume has been scrapped.