Is my mom being unfair?

So last week I bought a car. Or I thought I did. Essentially I signed all the papers and drove off the lot, but now they’re texting and calling saying I need a co-signer. I have good credit but my income isn’t high enough. I asked my mom to do it and she said she would, but if I missed one payment then she’s taking my car to keep for herself.

She even insisted I get a spare key made for her to keep.

She just bought a new car but doesn’t like hers that much and she loves mine. To me this is unfair. Not to mention, I have a credit score almost 100 points above hers, so it’s not like I would let that go down and bail on my payments, that’s not like me.

What should I do?