So a few things to note:
1.) you're not mixing your
GS all the way. This is bad. It must have a uniform color not only to cure properly, but also to work with properly.
2.) While it's a little difficult to tell from the color, the fact that you have those little patches where the
GS is rough and slightly pilly is a dead giveaway for the fact that you're probably using too much yellow. More yellow gives you more working time, but it also behaves more like regular clay (which is what your current attempt looks like you made it out of). Add in more blue, and it will give you a more plastickey feel which will be easier to sculpt.
3.) cloaks are very challenging. Taking this up as your first project is brave, but, as you see, unlikely to give you the exact results you're looking for. As stopleklinger said, the secret to free-standing clothing is layers, not trying to do it all at once. I'd like to direct your attention
here to my modelling page. Check out the two scratchbuilds and the three commissars (bottom to top is oldest to most recent), as I did a lot of clothing for these.
If you want something that looks exactly the way you want it, then you're going to need to cut out what you have and try again (probably several times) until you get your skill base up. Otherwise, covering the cloak in stuff to make it a ghillie suit is probably the best way to go.