Screwed up my only source of income

I quit my full-time job a few weeks ago for reasons and am currently looking for new work. I'm running out of money, and the only other income I have is a small office cleaning job, about $250/month. I'm supposed to clean this place twice a week and bill every two weeks. Due to depression, I have only been cleaning once every two weeks, but billing for all four services so they won't know I'm being so terrible. Well, of course one of the office tenants finally complained to the building owner who I bill to about the overflowing trash. I've screwed up here in a big way, and I need to know how to respond to the building owner about why I haven't been cleaning and still charging them. I've messed up so bad.

Apologize for the billing error-accept responsibility, offer to clean at no charge for the weeks you over billed. Then beg the owner to keep your job. Why did you quit your full time job?