Found this dog abandoned at the dog park a few minutes ago

I think it’s a puppy because it’s just sleeping and didn’t react or bark at my other dog. I was planning to take it to a shelter later today but my mom wants to keep it. What should I do? She won’t be back in town for a few more days. I live in an apartment and would probably get fined if they find out. Also, f$$k people who do this.