Now then, if you're casting from the bank or a platform on a pond, it sounds very much like you're simply not getting enough of the line behind you or forming a big enough D,V or whatever loop ( you could be touching the bank or other obstructions with your D loop, which certainly won't help.).
I cast a Scandi Compact from my 11ft 6ins Sage One and that's 33ft long.I usually couple this to 16ft of leader, either 10ft poly+ tippet or 10ft tapered leader and tippet.
It absolutely flies, in fact I've to hold on tight it go's so well.
In reality you should use the leader and the front few feet of fly line to anchor your D loop., with the rest of that loop held in a tight formation in the air off the water by the fixed anchor at the tip end of the line and by the variable anchor at the rod tip.
Your Spey cast should be a slow lazy sweep with your rod tip following a low plane, no way at all do you want to dip your rod to encourage a splash down!,as you proceed with the rod going backwards you want to plan the leader to touch down slightly upstream of your upstream shoulder by slowing the sweep slightly then by lifting the rod point to the 1 o'clock position up behind you.This will form your D loop underneath your rod point and allow ( very important word that!, ALLOW ) the leader etc to touch down 1st as the main portion of the line will still be moving behind you ( albeit at a steady pace! ) maintaining tension to the rod point and keeping your loop shape well defined.
At this point when your loop is cocked and loaded, you can risk a little lift onto your toes and a slight upward lift of the rod point to further tighten everything up, then your forward stroke( pull with your bottom hand 75% and 25% push with the top hand ) needs to be up n out.As your loop will be formed underneath your rod point, it will follow the rod tip up n out!.Like this it will encourage your loop to " fly" unravelling as it go's, dragging your running line too, giving you increased distance and better turn over and thus presentation as your loop will have chance to unravel above the water just before touchdown.
If you can source a Video/DVD by British casting guru Michael Evans, he recommends performing an in line roll cast time after time after time until you can plan how and where your loop will form, then still in the plain single plane you preform a " jump" roll where you lift the line completely off the surface and allow it to anchor just out from your body.Again time after time after time until you plan exactly where you fly will fall onto the water followed by your leader etc to anchor your D loop. Gradually increase the amount of line you work out as you go and slowly you'll get a feel for how to do what you should be doing.
Once you're cool with that then its time for the sweep up and round and again keep at it, because it will come and you will develop greater understanding as you are breaking the cast into its component stages, master one, move on to the next.
Best of luck with it all, and don't worry, most folk are just as frustrated as you at one point or another, it will come and in all probability you sound very close.
Yorkie.