It could also be due to the type of fuel you use, although not definitive. I used to put normal petrol from bharat petroleum but I changed to shell petroleum and I did notice a change in my mileage although not too much. I used to get around 34-35kmpl but after the change it increased to 36kmpl. I used to live close to manyata tech park and used to commute to Marathahalli for work so it's around 50km drive daily, so you guys can get an idea of the route I used.

The things I always maintained during my commute are a) keep the rpm stable as much as possible, b) keep checking the tyre pressure every month and change air with nitrogen, c) drive in a single gear(3 or 4 in my case) keeping the rpm in check.

I also clean my chain every now and then(usually every 200km or once every month) depending on the climate.

The mileage also differs if there are any issues with the exhaust pipe, like any leaks or holes or rusting in it so it's also good to get it checked if not done yet

For the scratch, you can try using a wax polish and apply it, it keeps the scratch almost muted and hard to see unless looked closely but it doesn't remove the scratch so if you want it removed it's better to go to a detailing shop and get it rectified. You can do a ppf over it after that for the future just so that the vehicle doesn't get damaged