The primary reason for crossing skis can be traced to several causes so no one solution can be offered. The three most common are rudimentary rotational skills, fore / aft balance, or lateral balance. In other words the three fundamental skill pools that help us create balance are typically where we would begin our investigation.To some this is not new news but before dismissing what I just said please read further and consider the following.
1. Twisting the skis, externally rotating your foot / leg uses a set of muscles that are somewhat weaker than the ones you would use to internally rotate your foot / leg. So if you are trying to simultaneously rotate both legs the stronger set of muscles can turn that ski a bit easier. So the solution in this situation is to match what the outside ski is doing to what the inside ski is doing. Simple enough in theory but what does that mean in real life? Consider the fact that lateral balance and weight bearing can have a profound effect upon rotary inputs and it becomes a bit more complex. The short version is that the more weight you have on a ski, the harder it is to make it pivot, or more precisely the same input applied to a weighted and relatively less weighted ski would produce different outcomes. This is why parallel turns at under a half mile an hour are so difficult but it is how to make very good wedge christies.
2. Fore / Aft balance, fulcrums and pivot points are all subjects directly effected by our fore / aft position on the skis. To further complicate this the inside half and outside half can end up at different stances because one leg is bending so much more than the other. If that's not complicated enough the two skis are at different points in their arced paths. Correcting for this has been debated here many times but what it has to do with this thread is that the skis may not be completely parallel during your turns unless you artificially force that outcome to occur.
3. Lateral balance, getting too far inside the turn forces the skier to balance on that inside ski. It also creates a higher edge angle because the skier's balance axis is tipped so far to the inside of the turn. So the outside ski becomes an outrigger and balance aid. So in this circumstance Edge engagement and the previously mentioned weight bearing are closely related and both contribute to unequal turning outcomes.
So what's the solution for you Albee? That my friend is hard to say based on the limited information offered to this point. I would offer that a scratch on your skis isn't a big thing and in many circumstances a natural consequence of your movements. Perhaps it's an error, perhaps it's not. What is important to understand is the alway parallel skis dogma is just that. Wider stances, making sure you get the inside ski out of the way, and even keeping the inside foot back to create more parallel skis, can and are often offered as solutions. But what are we solving? If the goal is perfectly parallel skis all the time I would question why that outcome is so important to you. Ifcrossing your tips / tails occurs all the time and you end up biffing because of that,then by all means correcting that is important. If it's simply scratching the topskins but your skiing is unaffected by that contact, it's not a big deal.