If you study regular sized synthetic bags rated at 20 degrees you will find that 3lb 3oz is a good weight for a backpacking sleeping bag in its class. It won't be quite as light or compressible as a down bag of the same rating, but it is much cheaper than a down bag.

As far as rolling the bag goes. You will want to either stuff the bag in the included stuff sack, or buy a compression sack for the sleeping bag and use it. I prefer using a compression sack as it will reduce the amount of space the bag takes up in your pack significantly.