How did Robert Falcon Scott get beat by Roald Amundsen?

Because Roald Amundsen was better prepared and had more luck than him.

That is a very simplistic way of looking at it.

1, Amundsen's route was shorter.

2, He had the better weather.

3, Amundsen's journey was simply a dash for the Pole. He did no surveying, no scientific work, in fact during the journey only two photographs were taken.

Scott's scientific work was that much that scientists only finished analysing it in the 1960's.