Do you think I should ask my dad if I could return the guitar he got me for Christmas?
Why did he buy you a guitar for Christmas?
He knows I wanted one. but if he doesn't return it I'm going to sell it to get a new one.
You seem to not like the guitar your dad got you, it happens sometimes. I hope you will still keep it out of respect for him even if it is not the exact same one you wanted. He might think you are ungrateful and then not want to gift you ever again if you get a new one now.
I will stop talking to him if that happens.
I'm sorry you didn't get the exact gift you wanted. Your dad was probably trying his best and you don't have to like everything he gets you, but it seems rude to want to return it. I know you seem to want something better but it would hurt your dad to know you want to take it back.