Hi Kasia, sorry for the delay. Your form looks fine, so I think it comes down to the fact that speed/accuracy takes time to develop. Check out the tips for practicing listed in this article.
You can use the on-screen tab viewer to loop a couple bars at a time. Start slow and focus on accurately hitting string two and one; and also focus on playing each note cleanly and in-time. Keep up the good work and let me know how it goes 🙂