just weight your front foot...that's it! You're thinking you'll catch and fall forward, but you won't. You are almost baseball sliding out every try. Also..I mean this in a positive, constructive way...stop being a pussy! You're movements look incredibly timid and scared, thus the leaning back, hesitation to land switch, etc. You're sliding a pvc pipe a foot off the ground, on soft grass, with a tarp...you are NOT going to hurt yourself! You could pop off the lip, spin as hard as yu can, land totally wrong on the rail, have a ridiculous Joe Pesci in Home Alone pratfall, and be totally 100% fine! Go try that, fall, see it doesn't hurt, than let the fear thing go to bed.
Also, let go of the gear shit. I know you've grown up a traditional skier who probably agonizes over every little top sheet chip or base gouge, but if you're serious about skiing park, you need to let that shit totally go.
Also, coming on NS and claiming being an instructor and telling everyone how great a skier you are and what a good jumper you are not only shows a lack of humility, but a disconnect from reality. Ease off that shit. You're tendency to lean back, even upon landing, tells a different story.
Just practice a lot. There are literally only maybe 3 "tips" you can get that are worthwhile, the rest is on you to apply them and build confidence and muscle memory. Straight sliding a rail isn't complicated or rocket science, just do it over and over again!