Fuel Tank/Gas Door story

So, I've been driving a 2007 Prius for about 2 1/2 years now and I do a lot of short trips, and living in Chicago my winter mileage is a tad on the low side (usually low 30's). On top of this, I hardly ever get much more than 8 gallons on a fillup into the tank.

In winter, I generally get down to one pip on my tank after about 225-250 miles. This is surprising, but I've gotten used to it. Due to the nature of my commute there are gas stations all along the way, but I usually go for Shell where I feel my mileage does a tad better than with other gas.

Anyway, because I fill up somewhat frequently, I usually go down to one pip and often don't fill until it flashes. The other day, I decided to fill up in the morning after going about 281 miles (a good tank) before it flashed at me - I dropped to one pip at 271.

I pull into the Shell and I cannot open the door to the tank. I keep pulling the lever and the door will not open. I don't want to scratch the car, so I head to work where I have my mechanic see if they can fix it without scratching the surface. As expected, on the way, my add fuel starts talking to me and the last pip begins to flash.

I get it there and they are able to fix it (I guess it was a cockeyed spring) and I did get to fill up before running out of gas.

The point of the story is that I've never had such an issue before (an unopenable gas door). Also the mechanic told me I shouldn't let it get so low.

Is that true? Do I need to fill up my high mileage car every 200 miles? isn't that too frequent?

I continue to be frustrated that I am at half a tank around 120 miles into most tanks. Seems crazy. Why can't I even get close to 10 gallons into my tank. It's supposed to hold 11.

I do not know. It just made me mad. Plus with the horror stories of prius' having serious damage when a tank is empty, I was seriously pissed at the sequence of events leading me to that situation, despite the fact that it ultimately worked out.