I reckon on the whole a very good effort for a first fly.
Most people would start off with something a little simpler than a WB so well done.
It'll catch just fine, but if you want to neaten it up a little bit, then perhaps after tying down pinch the tips of the marabou off so that they're all roughly the same length.
You could also tie in the rib & chenille a little further back, maybe 2 or 3 mm, the body starting where the bend stops is usual.
6 full, even turns of ribbing is what most people tend to get on longshank lures, so use that as a rough guide.
The hackle looks a little long for me, though this is personal preference. Be careful when you cut off the waste so you don't catch any fibres.
Just make sure you start off with an even covering of silk on the hook shank & everything that is tied-in is done so nice & tightly.
Finally, Dave Cammiss tends to use a couple of half-hitches to finish the heads on his flies. A 5 turn whip finish is much more secure imo, especially with a couple of coats of varnish on. A shame to tie a neat fly only to have it disintegrate head-first!
As I said, well done - not the easiest first fly.