You can't waive your right to OT pay if you are working over 40 hours per week. I'll repost my previous post.

If you work more than 40 hours in a 7 day pay week you must be paid 1.5 times your regular rate for all hours over 40.

And that is just Federal law. California law has even more situations where overtime is required...

Eight hours of labor constitutes a day's work, and employment beyond eight hours in any workday or more than six days in any workweek requires the employee to be compensated for the overtime at not less than:

One and one-half times the employee's regular rate of pay for all hours worked in excess of eight hours up to and including 12 hours in any workday, and for the first eight hours worked on the seventh consecutive day of work in a workweek; and
Double the employee's regular rate of pay for all hours worked in excess of 12 hours in any workday and for all hours worked in excess of eight on the seventh consecutive day of work in a workweek.