JETS first-round draft pick Mark Sanchez, who just signed a five-year, $50 million contract, is learning quickly he’d better be good. At the Samsung Four Seasons of Hope gala the other night, Sanchez participated in the traditional football toss with teammate Kellen Clemens and Hall of Famer Dan Marino, with guests bidding $750 to have a signed ball thrown to them. When his first try was overthrown, prompting groans and boos, WFAN’s Boomer Esiason told him: “Welcome to New York. You better get used to that.” Luckily, Sanchez’s second throw, spanning the Cipriani Wall Street ballroom, was good.