How did you word it when you 'gave' it to them? Gift or loan? That makes all the difference. You keep saying 'gave'. So it's the mom's right to re-gift it to whomever she chooses.
You can get a pretty SICK laptop at wholesale clubs for like $600 these days... it's an OLD COMPUTER. You'd probably end up getting rid of it in a year or so anyway. Tell your parents the truth and they will just have to understand that they raised a kid who has some manners not to try to retract a gift... that's worht something in and of itself.