Do you have a video of your throw? That would be extremely helpful to provide feedback of what's happening.
To speak generally on the topic, pre-rotations (rotor) tend to be very much a personal preference. As an example, here's a post from a few years ago that also included a poll:
https://slinging.org/forum/YaBB.pl?num=1590665970. As you can see the poll results were split right down the middle.
As David mentioned, something to try to do is make sure the rotation of the sling is in the same plane as the release. I will mention that this is not required. In the past I've used a more vertical rotation into a sidearm throw and did fine with it. But I do think having the rotation and release movements in a similar path can be helpful if you've having trouble.
Another thing is don't be concerned with your rotations being fast. A lot of times beginners will try to rotate the sling very fast, but this only makes the release need to be much more precise. And I don't mean to imply that a fast rotor is your problem, just mentioning it.
One more thing that often isn't mentioned, the pre-rotation also decreases the amount of energy needed during power stroke. The reason is obviously because the sling and projectile are already in motion. There's usually an increase in power during the final release, but the projectile doesn't need to be put in motion from a stationary position. I'll also clarify that I'm not saying one or the other is better, just that it's one of the differences.