I RARELY agree with car dealers but in this case all they did was sell you a car and take a trade in. You have no 'right' to change your mind and unwind the deal if you get buyers remorse. They can do that if they want to be great guys but they are under no obligation to do so.
Do not let them talk you into something you don't want. Do your research before you go shopping and NEVER make a decision without sleeping on it for at least a night, maybe more.
If they tell you - and they probably will - that the same deal will not be available tomorrow, just say, fine, and go to another dealer. There are many around.
Other dealers can tell you anything, talk is cheap.