You are under contract. You were under contract from the moment you accepted the offer verbally. Not having the printed version does not change this. Teachers apply for jobs all the time. Some get them, most, of course, do not. No one thinks anything of this. Unlike other jobs (because you have to provide cover for the days you're off), you can't keep the process secret so it feels different, but everyone has to do it. Your current head isn't in his first job. He applied for others, including the one he has now and he wasn't even allowed to apply for that until he'd done an additional course which he needed his then boss' permission to go on. Don't sweat about this. It is entirely normal.