it could be a series of unrelated events. i've bitten into seemingly good fruit only to discover its bad, and i've nearly been struck by lightning on several occasions. neither of which happened before, after, or during a spell. sometimes that's just life.
the crack in the title, you could of over looked it, but it could mean you used a lot of energy in your spell. another option, depending on what you did in the spell, you could of cracked it, if you put something hot on it, used something sharp, or stuck it for example.
i would make note of these things, but i wouldn't worry about them, because you might unknowingly curse yourself. a build up of energy can effect us, and worrying will build up negative energy. every time you break a glass, or stub your toe, you might go 'oh no, its a bad sign' and slowly cast a spell on yourself. our thoughts, words and action can cause things to happen good or bad, so try and watch what you do or say. its like when you're sad, you keep thinking about what made you sad and before you know it you feel worse and worse. same thing.