Don't just go off the trip computer. Mine reads over by about 1l/100km, and with your 20" wheels it could be worse for you. Make sure you fill it up, run it to close to empty, then divide the litres it takes to fill by the kms travelled. e.g. 62l / 360km = 0.177 (17.7l/100km).

If your getting 320 from a tank, that is more like 19 - 20l/100km, not 22l. Doing short 2k trips to the gym and back aren't exactly the best economy runs.

TBH i don't really think theres anything wrong but it's good practice to change the HEGO's anyway if you don't know how old they are.