@Am716, to carve comfortably on any terrain, you'll need to work your way through several steps.
1. First, you'll need to override the old habit of pivoting the skis as you start the new turn. This is the rushing part of what your instructors are telling you. It sounds like you always pivot the skis to point down and across the hill as you initiate your turns (most people do). Replacing this habit with tipping the skis and waiting for them to turn is in itself quite difficult to do. That's because so many people can't feel themselves pivot the skis. It's not so much fear or lack of knowledge causing the blockage, but the strong persistence of the old pivoting habit that keeps it in place and destroys any potential for a carved turn. Know your enemy! It's the pivot.
2. Carving makes the skis go fast in the direction they are pointed. The metal edges slice their way over the snow, and the tails follow the tips, scribing a thin line in the snow. This is FAST. That's why fear creeps in, and when fear is there, the pivot creeps back in. Carving speed can be shocking and frightening at first, so people bail and pivot the skis to point across the hill when the carve starts. So learning to carve needs to be done on stupid-flat terrain, with barely any pitch. Learning to carve on green pitches is difficult; go to the bunny slopes instead.
3. When on that beginner terrain, head straight down the hill doing railroad tracks. This is done by tipping both skis together starting with the ankles. You say you do railroad tracks. Great! Keep doing that. Do it again and again, until it's easy to get pencil-thin lines in the snow without wobbling and falling. When the speed gets too fast, abort and start over. You'll have little to no speed control, and that's OK. Just focus on tipping the skis and
not pivoting, leaving those lines in the snow. Let the skis turn you. Once you figure out how to tip both skis with your ankles, without pivoting, and to balance on those two tipped skis, and to let the skis turn you, you'll still gain speed and get going faster than you are used to even on nearly flat terrain. That's OK; just stop, then start over.
4. Once you can make the carve happen on flattish terrain with those tiny railroad track angles, you'll need to learn to carve rounder, more completed turns. Completed turns are your first method for doing speed control. Completing your turns to almost point uphill will keep you from gaining speed as you head toward the lift. Teach yourself to shorten the inside leg more, bringing its knee up to your chest. Morph those railroad tracks into completed turns this way. On the bunny slope. This short-leg-knee-up-to-chest will give you higher angles, and will help the skis come all the way around. You'll need to work on balancing on the outside ski as you shorten that leg, or you'll fall over. Focus on letting the outside leg hold your weight while the inside leg is shortening. NO PIVOTING! Your turns may be pretty wide, so you'll need empty slopes to learn this on. Do this on the bunny slope when it's empty, and progress to empty low-pitch greens. Your goal is to not gain speed as you get lower on the hill. You'll still be going very fast in each turn, just not gaining overall speed as you finish the run. Carving is inherently fast.
5. A second way to do speed control is to shorten the radius of these fast, carved turns. This involves bringing that inside knee up to your chest
faster. This will get your skis on their downhill edges before they point down the hill. Consider this an advanced skill. It can help you not be dangerous to self and others on blue-green terrain. Carve only on beginner and green pitches until you've gained this advanced skill.
6. This whole progression assumes certain things about your gear and your snow. Are you skiing on midwest/eastern hardpack, or western natural snow? What skis are you on? Are they wide, rockered powder skis, park twintips, or frontside carving skis with camber and short radius built into them?
7. You want to carve. Is this because you seek speed, or because you want to start racing? Or is there another reason?