Hello Mira.
I actually watched your AVOYP video of the Aerial’s RIff and noticed many things that I wanted to give you advice on. From there, I wondered if you have posted other AVOYP, searched your history and found this topic - which is you asking about the very issues I wanted to comment on. I have taken screenshots from both of your videos.
My overall comment would be that you need to reset your entire body and hand posture when playing.
[1] _ _ _ _ _
This picture shows you holding the guitar at an angle, leaning it in towards your body. The guitar itself needs to be held in an almost vertical plane. I’m not sure what sort of chair you are sitting on. You need to be upright and comfortable in a chair with no arms. The guitar needs to be pulled in to an upright position. Cuddle it close like you love it! 
Something like this.
- -
From that shift in posture and position you then need to wrap the elbow of your strumming arm more around the upper back part of the guitar body. That can be seen in the last pic above. Your forearm is resting on top of the body and your elbow sticks out behind the guitar. That makes the actual mechanics of the strumming movement very difficult. It forces your hand away from the strings which has the undesirable and uncomfortable effect that your wrist has to be forced to work at an angle, aiming it and the fingers back in towards the strings. Look at the pic below to see how big a gap there is between your wrist and the guitar body. By hooking your elbow around the guitar your forearm will more closely follow the surface of the guitar body, your wrist will lie in a more comfortable and flatter plane for optimal motion up and down as it swings in short arcs for strumming.
[2] _ _ _ _ _
This shows again the extreme angle at which your guitar body is held. It also shows another issue I would recommend you address and try to break the habit. You have curled up and tense-looking fingers in your picking hand. Try to allow fingers 2, 3 & 4 to relax, stretch out a little bit, fall from the tight curl they are in and ease your hand tension.
[3] _ _ _ _ _
Holding the pick.
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This picture shows the amount of pick that you are allowing to protrude beyond your thumb and 1st finger. Justin does mention to beginners that they can allow a reasonable amount to stick out - allied with a recommendation that they use a very thin pick. Your pick is very thick (1.5mm) and you are not a total beginner. You need to bring the pick much further inside of the grip and have only a small amount of the tip sticking out. I also recommend trying thinner (not thin, just thinner) picks. 0.5mm-0.8mm perhaps.
[5] _ _ _ _ _
This shows that your 1st finger is being held very straight from the first join to the tip. Try to curl it around fully from both of the joints. See the next picture showing this grip.
[6] _ _ _ _ _
This shows the direction of your strumming as your pick moves across the strings. The way your body posture, arm position, wrist angle and grip are all working, your strumming is moving in the direction of the guitar bridge on the way down. Your pick is also going in too deep as it moves from one string to the next. Instead of gliding across the surface and just stroking the strings it is clashing into them and ‘digging in’ which makes for a strumming and picking sound that can be jerky and not smooth.
You want the movement of your forearm, wrist and fingers to follow a shallow arc across the strings something like this.
Your arc has your hand and pick moving in this sort of arc.
I hope that helps.
Cheers 
| Richard | JustinGuitar Approved Teacher, Official Guide & Moderator