Back extension is incredibly important in the Pilates Mat work. But, as you will see in the Swan on the Mat it is not about how far "back" you go but how long you can get! Focus more on how long you can maintain your lower back, fight against gravity with your center and how far you can pull your heart forward. The Swan has several variations so pick the one that is right for you today. And, instead of focusing on how "big" your Swan is focus on how long your Swan is! That is where you will find the strength!
Press your hands down and energetically back, pull your heart forward.