Ratchet---the Concorde stretches about a foot in length at Mach 2, due to how hot it gets. All planes stretch a bit when they're that warm/fast, but the Concorde does notably so due to its extreme length and shape. It's not so much on a 40ft jet as on a 200ft jet. Similar to how an SR-71 only achieves its "true" shape and the fuel tanks seal once it gets going hot and fast.
PS--and a point is, that FEW planes can beat the Concorde. Yes, there are some out there--the fastest planes ever built. But the sheer fact that a PASSENGER plane can go faster than 90% of military combat interceptors can--is pretty remarkable. That'd be like if Ford made a family sedan that could out-race 90% of Indy or NASCAR.