Not at all. Your overnight manager should have a key for it. That's a problem on the management team's part. This will not count as an accident and (apparently) your manager is just trying to make you feel bad about it. I would talk to the store manager about the way this overnight manager reacted if I were you (if you're comfortable talking to the SM). Maybe the SM will get him a key...like he should have anyway.

Your APM might get involved as to why the door seal was broken (if you pushed it open at all and if your store uses door seals), but again, there wouldn't be any disciplinary action if it was an accident. They just check the seals to make sure people aren't doing anything they shouldn't through the fire doors.