Wondering what mistakes you might be making when you're learning whitewater kayaking? Here's a helpful and funny video from the Unsponsored kayaking blog. (There are a few good pointers after it looks like the video ends, so keep watching until the actual end.)
Just for perspective, one of the best kayakers I know (Darcy Gaechter, co-owner of Small World Adventures in Ecuador and author of the book Amazon Woman) says she likes to always have a little side to side lean in her boat, but she has great balance and is always really centered regardless of whether she has a lean or not.
Basically, boat lean can be used as a tool in various river situations, the point in this video is that you should have control over it and be able to keep your boat level when that's to your advantage.
Speaking of Darcy Gaechter, she was the only woman in a 3-person crew that was the first ever to paddle the Amazon River from source to sea a few years ago, including through gnarly Class V, active dam construction sites and areas controlled by drug traffickers. Amazon Woman is Darcy's book about the trip and I highly recommend it - the Audible version, which is what I picked, is really well narrated.