In blank paper ticket you will be charged for highest class or type of train you are traveling. In some routes I had traveled in which my connecting train had only 2S or GS and CC. My primary ticket was of SL but I had to paid for entire journey for SL base charges and even SF if required. In your case you had been charged 320 per person as SL base fare for entire 615 kms. If you have any connecting train on your route as M/EXP then you are permitted to travel in SL without any extra charges.