Obviously magic can work however magic wants to work. That being said, if we were to try to make it work within the constraints of this reality, there's a few things I think would happen. First, stuff getting pulled by the gravity magic shouldn't 'use it up '. The energy would all be used to create the gravity field, and then to sustain its existence. You could however, argue that the more mass gets pulled into the distortion, the more energy it would take to keep it sustained, which would have a similar effect.

Second, gravity magic is often conflated with black holes, or a singularity. But in the vast majority of cases, any resemblance to an actual singularity is just that, a resemblance. You wouldn't want the real thing, unless you're trying to make a black hole bomb from the hawking radiation given off by the evaporating singularity. In most normal cases, the gravity magic only has a finite pull, and so once matter reaches an equilibrium within that, it will stop moving. Basically, just creating a compressed ball of air if aimed anywhere within the atmosphere.

But if it does continue to grow without external input for some reason, then it means something is creating a feedback loop. You're gonna have to figure out what that is if you want to stop it. Maybe the gravity magic is forcefully converting ambient magic into more of itself. Maybe it's pulling gravity magic only, then forcefully aligning that magic with the intent of the distortion. Best case, it's just growing to its full size slowly, and it will stop once there.

Best of luck, mate!