The company must pay you overtime for work over 8 hours/day or 40 hours/week. Period. The California Labor Code specifically provides that an employee may not waive his right to overtime through an agreement with the employer.
It sounds like your overtime claim is relatively small, so it probably will not be worth your while to hire an attorney. You should contact your local Labor Commissioner office (officially called the Department of Labor Standards Enforcement) to file a wage claim against the company.
Good luck to you!
Since the employer considers you a non-exempt (hourly) employee, you are certainly entitled to be paid overtime premiums for all hours worked in excess of 8 in a workday or 40 in a workweek. So, yes, you have the right to file a claim as suggested by my colleagues.
The problem that I foresee is in proving the hours you are claiming. You say you worked overtime every day but signed off on having worked a 40 hour week. Assuming the employer will deny you worked overtime, the burden of proof will be on you to convince a trier of fact that you actually worked the hours you are claiming. If you have any documentation or witnesses who can verify this claim, that will help you. If it comes down to your word against theirs, you are going to have a problem. Sometimes talking it over with an experienced employment law attorney can help ferret out what kind of evidence may be available to support your case. Good luck.
They say you get what you pay for, and this response is free, so take it for what it is worth. This is my opinion based on very limited information. My opinion should not be taken as legal advice. For true advice, we would require a confidential consultation where I would ask you questions and get your complete story. This is a public forum, so remember, nothing here is confidential. Nor am I your attorney. I do not know who you are and you have not hired me to provide any legal service. To do so would require us to meet and sign written retainer agreement. My responses are intended for general information only.
Whether or not you are in fact a non-exempt (i.e. eligible for overtime pay) employee depends on the type of work you perform (i.e. factual analysis). What type of work do you do? The fact that you are paid by the hour is supportive of your argument that you are owed overtime. Assuming that you are in fact a non-exempt employee, the facts you presented above shows a clear violation of wage and hour laws. In California, you are owed overtime wages if you work EITHER over 8 hours a day OR over 40 hours a week. Your employer has a duty to keep accurate time records of all of the hours that you work. Moreover, as a non-exempt employee, you must be offered an uninterrupted 30-minute lunch break for every 5 hours worked as well as at least a 10-minute rest break for each 4 hours worked. Your employer's failure to abide by these wage and hour laws subjects your employer to statutory penalties as well as attorneys fees should you succeed at trial. You should consult a lawyer to discuss your options of filing with the Labor Commissioner or a formal legal action.
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.