Don't worry, Catrin- I've been MTBing ~10 years and I didn't really get the whole momentum thing until just last year. Always something new to learn!

You will have to steer some on a turn that sharp. But the slower you're going, the more you have to steer and the less you can lean/corner. I suggest finding a sweeping turn that you're comfortable with (no edges!), and practice going through it at different speeds and changing up the amounts of steering and leaning. See how your body and your bike respond.

Good luck!