I'll try to offer something which may not have been already mentioned here, simply that if you're blowing your anchor, it's most likely due to making the D-loop sweep too fast. Try slowing it down so that your anchor is where it needs to be, the D-loop has formed and the line is not "stuck" in the water next to you, nothing more. For novice casters (I was there myself), it's difficult to trust that the skagit head and its rather small D-loop will be sufficient to cast your rig but it is. Having that anchor where it needs to be, well-planted below the surface, will enable you to make a powerful forward stroke with zero possibility of being blown on the backward sweep and that thick skagit line will do its work for you once its set in motion.
You'll find that with practice and a better sense of timing, that the cast will happen with almost no major effort. Like golf, it seems that trying harder does not render a better result. Be realistic in your objectives too, as most fish are caught within 50-60' of you and casting further is rarely needed. You'll get there, just keep practicing and maybe get a lesson or two before some bad habits form. Good luck.