Why is my plant doing this?

Imo cut the top fan leaves as they are blocking light to the lower bud

 

What is it doing? That's a happy posture for a plant.

 

Those fan leaves are feeding that top bud. Look at the structure of the cannabis plant. There is a fan leaf directly underneath every top shoot that feeds it. When I lollipop and prune or whatever I always remove the top that goes along with it if I remove the fan leaf. The main top will still get fed from the main stalk but it will slow the development and final size of the main top if you remove those leaves.

Are you running out of headroom for the light? I would bend the whole plant over like a banana with a fishing weight and a string or any other material you like. lower the light so it continues to be perfect distance to the majority of tops and within a day or two all the tops will turn back up towards the light. The other thing you could do is pinch the main stem about 4 nodes down a few times to weaken it and bend the main top off to the side as close to 90 degrees as you can get it. You want the stem to fold without breaking. That's the idea of pinching it. If it does break a little no big deal put a bit of tape on it and the main top will finish anyway.

Cannabis is more tolerant to breakage then any plant I've ever seen in my life. You can literally break a branch more than halfway across the stem, put a little tape on it, and it won't even wilt. It will heal up and be stronger than the other branches in the end. I've never ever killed a branch even breaking several. A little tape and a prayer and it's all good.

 

That's the happy dance, no problem
Does my plants stance look familiar? About the same happy leaves

 

I will make it simple . what do you do when your cold and you u get to sit in the heat ? or when your in the shower . you stretch your self towards the heat if you will it feels so good . the plant is doing the same its liking the light so much the leaves stand up little solar reflectors turning to get as close to the light as possible

 

Looks like you're 3 weeks in 12/12 to me. Almost the end of stretch. It will only get a little taller and fill out from here. Depends on the strain.