Emily, for what it's worth, a buddy of mine with a new M3 Standard Plus delivered 12/31/2019 is also seeing only 60% of expected range during his first month of ownership but that was due to his 285 Wh/m average (higher than what I average in my Model S).
To get the EPA rated 250-mile range on your Model 3, you need to average 216 Wh/m (54kW battery). At 249 Wh/m, you're already 15% below EPA. I'm in Northern California and even though the climate is temperature the mornings are still cold, and I expect the same for you in San Diego. Unless you're warming the battery while plugged in, you could be using a lot of energy just warming the battery during the morning drive. Also, check is you have Smart Preconditioning on, and use the seat heaters instead of the heater. Also, if you have larger wheels then that can also cut your range by 10%. In my S, downsizing from 21s to 19s netted a 12% improvement in Wh/m. Good luck and hope you are able to enjoy the car more. The 3 is a helluva car for the money!