Hero Motocorp — Bike mileage problem..

Address:

Gaya, Bihar, 823001

I have purchased hero hf deluxe in april 2016, i m facing issue of mileage since purchased, i already complaint to hero agency but mechanic says that your mileage is alright. But average is still 35-37 km per litre in my knowledge. What can i do. My bike no is BR 02 AD 8109. 4 free service completed. Meter reading is about 4200 km. Problem persist.