I need legal advice? I work at Target.?

I work at Target. I was recently asked to cover a department and was told by current supervisor that someone would relieve me before I finished my work day without a break. Now I am being penalized for going over the hrs worked without a break and I feel that it was the supervisor that needed to cover me while I went on my break. Now I have to complete another 12 mths of probation because I was penalized, they also want me to sign a doent in which it indicates that it was my fault, when it was my supervisors call to relieve me. I feel like Target and the supervisors are going against the california laws and are making me feel like it was my responsibility to leave the department unattended to go on my break. I went to our HR department for advice and all I was given was scrutinizing allegations that it was their word against mine and that I should of known better. I need istance because I do not want to repeat my probationary period once more.