This giant asteroid is the size of an entire planet

If it's on the same size of a planet, why is it still an asteroid?
By definition, since to be a dwarf planet or planet, the body has to be massive enough that its own gravity causes it to become near-spherical.
Also, with that much of mass, it'll be pulled by the host star's gravity, thus creating an orbit.
But well, this is fiction. Anything's fair 😁
Go for the next chapter!