Is it possible that i burned 550 calories in 50 minutes?

Yes, just heat units: If you were within an insulated 550 liter water bath at a known temperature, (evaporation temp changes were also blocked) and, in 50 minutes, the water temperatrue increased by precisely 1 degree centrigrade, they you would have burned ; released into the water 550 kilocalories (1, 000 little calories; kilocalorie is the unit used for human foods) of enegry.