More than likely, you overestimated your activity level. Another factor is your current weight. The more a person weighs, the more calories are needed to maintain that weight. So, to lose weight, you might not have to eat a really low-calorie level.
I agree that 3600 calories seem high for weight loss for a person of your height. Go back and adjust your activity level. You can also reply with your stats to me so I can verify your results.