It shouldn't be a problem this early, but magic does build if we don't use it. Bonding with a monster will help balance it out but until you do, be sure to practice. The more you're using magic, the lower your reserves. That might normally sound like a bad thing, but it's a lot like a kettle: if the steam's not released, it will explode.

[ It's a simple, truthful answer without any of the hidden jabs behind it. A witch that's losing control benefits no one, and Light will genuinely work to assure that won't happen. ]

I don't mind giving you some simple spells to practice, but this isn't the place for it. Beginning witches have a lot of time predicting and controlling their own power.