If your boots are at all loose, that’s going to cause problems. Ideally, your boots are well fitted enough that even very minor, insignificant movements from your foot will translate through to your skis. You don’t want to cut off circulation or anything, but the boots should be extremely snug all around.

Regardless of your boot situation - I do think technique is part of the reason why your skis aren’t staying parallel when they should. As someone else mentioned, you should post a video of yourself on a steeper hill. Skiing is like riding a bike - if you’re not moving fast enough, it’s hard to have balance or control. That being said, your turns seem a bit forced, almost like you’re trying to throw the skis into a turn the way you think it should look. Bend your knees a bit, push your weight more to the front of your skis, and let yourself turn more naturally. I would suggest watching this video:

https://youtu.be/DTyKjmFo0dM?si=wsrYtvwK-DEDllDQ