Return a Travel System to Target

Tonight me and hubby bought a graco travel system, we opened the box and assemble it, it's so nice and in perfect condition, I love it a lot but for some reason we have to return it. I do have the reciept with me but I am worried cause we already have opened the box and it is assembled. Are we going to have any trouble about it? And how will I return it? Should I put them all back in the box? Cause I also have read that some return them without disassembling and the store will do it.đŸ˜« Anyone who have this kind of experience too?