Oswald most likely was looking through the scope as he began to try to track the moving target.
Why in the world would former sharpshooter Oswald have been looking through the crummy, dimly lit scope?
If he had "tracked" JFK's head through his scope as the limo was coming straight towards him on Houston Street, he not only would have been spotted by the Secret Service agents in the follow-up car, but would have shot at JFK's huge, looming, enticing-through-the-scope head.
However, if he *was* "tacking" JFK's ever-more enticing head through his scope while the limo was still on Houston Street and 1) the Secret Service agents *somehow* didn't notice him and 2) he *somehow* resisted the temptation squeeze off a round at JFK's large, looming, ever-enticing, impossible-to-miss head, when the limo started turning onto Elm Street, he may have tried to switch over to his much-more-practical-at-that-close-range iron sights and . . . gasp . . . . lost his bead on JFK's head in the process.
If he *didn't* switch over to his iron sights when the limo turned onto Elm Street but stupidly continued "tracking" JFK's head through his scope, that in-and-of-itself could explain how he managed to miss everything with his first shot.