It looks like you are doing a good job keeping your left hand fingers on their tips! Try keeping your left hand wrist straighter. It looks like it is bending a bit. It also looks like you might be holding your violin too high. It should be at a very slight angle down, so make sure you are not holding it up any higher with your left hand. A couple tips for your bow: keep your bow pinkey bent. I would also recommend playing some bows on open strings while watching in the mirror to see if your bow is lining up with the f holes to keep your bow straight rather than relying on the bow guard around your violin. Just by doing some straight bows on the A and E strings while watching in the mirror can help get the muscle memory into your arm.
You’re doing awesome for 3 weeks! Keep it up! Let me know if you have any questions! I am available here if you want more one on one help. http://violintutorpro.com/private-lessons/?show=details&performer_id=4407