Maths does help describe the Universe, it's true, but in a way that's purely coincidental. Maths is also capable of defining abstract objects that have no relevance to reality -- or, at the very least, no relevance to our ability to measure it.
For example, the question of whether or not the Universe is literally infinite in size is certainly impossible for us to determine one way or another: we'll only ever see a small piece of it. But mathematics can describe infinities, of many kinds, with no trouble.
Likewise, our ability to describe reality at small scales is almost certainly constrained from below: the "Planck Length" scale may or may not actually matter, but we're almost certainly not going to be able to physically measure units of distance smaller than it. But, again, mathematics is unconstrained by such considerations, and can describe units of distance as small as you like -- and then smaller still.
So, for sure, Mathematics can be used to describe the physical Universe, but it also describes many other things.