I want to sell the christmas present my mom gave me
Why do you want to sell it? Did you not like it?
Because... I don't know, I do not really like it that much
it's normal to not like the gifts that someone has given to you, I have also experienced that. But that gift was given to you by your mother, and selling it is not a great way to show your appreciation towards the gift. If you do really want to still sell it, make sure that you ask your mom to see if it is okay with her and make sure that it doesn't hurt her feelings.
Oh I know
You could always ask your mom to return it and ask for something else. Asking to return a gift is normal and your mom might feel better if you do ask her to return it so she can get her money back for something you'd like.