Sounds like your bid was way too low. There 'is' a reason you got the job and most likely the property manager saw a opportunity to save 30k and take you to the cleaners. Even guys with many years and previous experience with these types of properties struggle over their final bid to turn in.
On paper, senior living neighborhoods don't seem too bad. You probably thought to yourself, "not much grass, and we can knock the trimming/edging out fast" These places are riddled with walkways, curbs, patios, fences, and many more obstacles that someone without the experience wouldn't see due to the high emotions of 'scoring' such a 'great' job.
These places run much smoother when you can 5-6 Mexicans doing each lot like an assembly line.
I am surprised to see you last 3 years. I probably would have lasted 3 months.
The positive thing is that you seemed to have learned from your experience and are restructing and reevaluating what you can and cannot do. Furthermore, what 'you' 'want' to do.