/sci/ - Science & Math

I am a math undergrad at ucsd. I am currently taking my first upper division course in upper level math called intro to proofs. I am getting a B in this class. My dreams are to study mathematics and get a phd and work in academia. I have been used to getting all A's in my lower division courses, but this class has hit me like a brick. What is the possibility of me getting into UCSD grad school for a phd in pure mathematics given this information. I suppose the better question would be how good does my GPA have to be in order for me to have a chance. I am kind of pissed off that the class average on the midterms was 65%. I know I should just study harder but I need the assurance of people on a Polynesian wood carving forum because I am a weak minded simpleton. I apologize for off topic.