Hi Liliana – sorry for the tardy reply! Gabrielle is away running some workshops and so we only just got a chance to discuss your issue & reply!
Basically you should just be staying in stage 2 (ie don’t force the knees) until you can keep your knees down with only moderate effort or preferably, not even thinking about it.
Something you CAN experiment with though, to assist this process is to widen the knees to allow you to get from stage 2 to 3 without the knees popping up at all. Same applies on exit – it’s OK to widen the knees (leave the head hanging back) as you come back out.
It can be a tough pose on the knee joints and you don’t need to add any extra pressure!
Hope that helps – if not, keep asking the questions!
Namaste
Robert