Hi Liliana
As long as you have the lift incorporated in your hips (and also try to make it radiate through the lower half of your back to go up, up, up) then you should really be OK. But just checking with you, do you feel any resistance to the upward movement? Is it at all possible you are dropping through your hips a little in order to feel the stretch in the arms or by focusing on the push down of the legs? The geometry of this pose would generally dictate lumbar and lower thoracic opening.
Feel free to add more distinctions!!!
Namaste
Gabrielle 🙂