Job offer and I accepted but now am reconsidering..?

I got a job offer as a bank teller at $12/hour which is what I put on my application as desired pay. To my surprise they offered the position to me with that pay. Now I am realizing, however, that since it is a full time position and I am a college grade I should have probably asked for more. I am wondering if it would be alright for me to call back and try to negotiate the hourly wage even though I already accepted the offer at that pay. Any advice??