I was recently offered a communications job for a state-wide health care services provider. The HR manager called me, offered me the job, and told me the hourly rate. I was in the car at the time so I asked her what the hourly rate would work out to over the course of the year. She did the calculations for me and it sounded good. She asked me if I wanted to move forward and I said yes (I'm not sure if this is considered formally accepting).
Then I got home and did the calculations myself based on the hourly rate and I realized that she had miscalculated by about 10%, meaning she had told me a yearly amount that was 10% higher than what the actual amount would work out to be.
This happened on a Friday. Am I able to go back on Monday and renegotiate the salary? I'd like to get something closer to the total yearly amount that she told me in the phone conversation. I'm worried though because I said I would move forward, she did give me the correct HOURLY amount, and the yearly amount was only given verbally, not in writing, so I'm not sure if there's a record of it.
How should I proceed?