Am I not paying enough attention?

So I did the Day 3 practice and really enjoyed it. I guess it's my favorite from the 5. I tried to really take it easy and not push too hard. There are a lot of lunges to prepare for the backbends and although I do use a blanket below my knees it still feels a little uncomfortable. So this is one thing I have to be careful about. The second is that after the practice my lower back feels a little sensitive. I'm not sure if this is normal or I'm again going too far? I really don't think I did too much. Maybe because of my knees I didn't pay enough attention on my low back during lunges? I must say that the practice is perfectly sequenced - plenty of preparation and then release of the back and relaxation. So the only thing that could go wrong is if one is not listening to and respecting their own body.