For a first attempt at a parachute that is a very good fly. When I tie parachutes I always form them without a head at all. This is not as difficult as it seems. Tie in your post, tails and body. For parachute posts I also use poly yarn of one kind or another. I tie the yarn in around the hook shank and secure in place with turns of thread. Like this (this is an example from the tying of a Klinkhammer).




How much yarn should you use? If you twist up the yarn into a tight rope then measure it against the eye of the hook it should be wider than the hole but no wider than the outside diameter of the eye. This is for a post where the yarn is doubled, so if you tie your post along the hook shank double it over.
Once you have tied in your body take the thread to the eye and dub back to the end of your body. Then tie in the hackle to the post, wind it and whip finish under the hackle around the post.
You may find it much easier to turn the fly so that the shank is vertical and the post horizontal.
Always wind the hackle so that each turn of hackle is made "under" the previous turn. That is between the previous turn and the hook shank.
Hope this helps. You have already discovered just how good parachute flies can be so keep trying.
Cheers,
Alan.