I had something similar. When a friend came to stay, he made a big iron burn on my living room carpet, right in front of the fireplace. On his own initiative, he went out and bought me a rug to cover it up.
Unfortunately, I was aiming for a white, green and silver colour scheme in that room and the rug he bought me was black, white, red and orange. Maybe one day, I’ll move somewhere bigger and can make use of that rug, but at the moment it’s rolled up under my bed.
I’m amazed that several posters have called your rug “hideous”. It’s in neutral colours and although I’m not a big fan of quotes (and the text is a bit close to the edge), I like the moon and stars theme. The moon isn’t actually back to front, it’s a waxing crescent. I can’t imagine that rug clashing with many colour schemes to be honest.
However, as it’s not what you wanted, I would move it to another room and use it as a playmat. I agree with telling MIL you were afraid you’d trip on it in the dark.
And I agree that buying furnishings as a gift is usually a very bad idea.