1) manual or auto? engine capacity? (1.3 or 1.5) carburetor or fuel injection?
high rpm will definitely consume more fuel, if carb, you can consider tuning the idle yourself via guide from saga/iswara thread or google image.
auto idle is ~850-900 while manual is ~800-850

2) yes, that is correct. if you suspect is the gun issue, consider changing other stations. also the 45liters is only the tank, and the minor "overfill" could possibly be the tubes/passageway. btw, did it spill out from the fuel port?

for your references, this is my FC: http://www.fuelly.com/driver/quazacolt/saga
so in *my opinion* you actually have damn good FC

1. 11.4km/L is good on a 1.3 (underpowered) manual in the city. I would love to know how you used to get 14km/L. That is really good for the 1.3. the 1.5 magma iswaras can do that with no problem. But the 1.3 is severely underpowered thus making good consumption hard to achieve.

2. On a totally dry tank, you should be able to squeeze in like 46L++. The tank may be 45. But you got your filling port and piping etc. That more than a liter right there.

Notes:
Car still running after you swith off your key means your engine is self combusting the fuel. That could happen under 4 scenarios.
1. Your compression ratio is too high (not possible)
2. Your engine is too hot (is your cooling system working?)
3. You got contaminated fuel in your tank (think kerosene etc) - most likely
4. Your spark plugs are so fouled and carbonized that they have become glow plugs of sorts providing a combustion source even when the spark has been cut off. (when did you last change your sparkplugs? are you losing engine oil?)

Petrol engines use spark plugs to combust each stroke as the compression ratio does not allow the fuel-air mixture to reach self combustion conditions (diesel engines do this...they do not have spark plugs)

The 1.3 manual is a carburatted engine. All carburatted engines have a little reservoir of fuel in the carburettor. So if your engine keeps combusting on each stroke even when the key is turned off (no more spark plugs, fuel cut-off solenoid is closed) the engine will keep running and sucking in fuel from this tiny reservoir until it is dry.

They shop may have said its the auto choke. I have heard of this before. But usually you have to change the bimetallic strips if the autochoke goes bust.

Have the engine advance checked. It usually doesnt run out but having it checked out every 50,000km is a good practice. If this is out, your consumption will be quite significantly affected.