Should I ask my girlfriend to take it down a notch?
That seems weird. What is causing you to want to ask your girlfriend to take it down a notch?
Because I don't like her anymore.
Telling her to take it down a notch seems a little rude if you asked just like that. If you feel that you do not like her anymore then you should not be in the relationship. It would be worth the time to explain to her how you really feel so she doesnt have to feel like she is walking on stones with you.
I don't want to ruin what is left of the relationship.
It doesn't seem like the relationship is working out. You should stop trying to control her and end the relationship instead. It would be better for the both of you.