I'm going to drop my gf off during a red light not the spot she wanted
Why would you drop your gf off somewhere else than the spot she wanted?
She keeps asking me for rides and it's annoying.
Well than say no to begin with. If you're not going to do the favor than don't say you will. You are expected to help your partner in a relationship.
I don't know how to say no to my gf.
I think it would be good to tell her how you feel and set boundaries. Maybe she can't afford a car you can let her borrow the car if she needs it for a bit.