Hi Carrie.
I think that Empyrean's comments were excellent, and I don't have too much to add, but I wanted to chime in on this because I had this very same problem for a long time, and to such a degree, that I eliminated the shoulder mount from my collection of moves entirely for a long period. Once I got to the top of the shoulder mount position I would begin to feel unstable, scared, and not know what to do next. So once the anxiety settled in at the top of the shoulder mount, I would ferociously grab for the pole with my legs in order to avoid the feeling like I was falling.
I've recognised a few reasons why this was so. The first one is that I was afraid of the pain that would be caused by rolling over my collar bone to finish the inversion, and I didn't know how to perform this mount without doing that yet. I didn't know that once I had my legs on the pole, I could tilt my hips toward the pole and push away from it with my arms, so that my collar bone wouldn't have to support the weight of my entire body for that moment. The second reason had to do with my grips. Sometimes I would be using momentum to perform this inversion, which meant that once the momentum became inert, I was relying on my hand grip no matter what position I was in, even if it wasn't prepared. In other cases, I relied on my body weight counterbalanced against my palms on the pole, so that once I had come out the upside of the Shoulder Mount there was less weight on my palms and therefore less friction, so my grip did not feel safe anymore. In this situation, I would do the same as before, grab desperately with the legs in a way that was ugly, uncontrolled, and not really even efficient in terms of balance or safety. Additionally, when I would do this, I would put both of my legs on the opposite side of the pole in exactly the way Empyrean wisely cautions us not to do! Last, I really didn't have good ideas about transitions from the shoulder mount. Even though I knew how to use some inverted positions, I didn't know how to get into them from the shoulder mount. If only I had so much nice guidance when I was learning this and other moves... *sigh*. The smart solution in both cases was a stalled hold at the top of the shoulder mount, where my torso would be about 45 degrees of the pole and my legs would form a V parallel the floor.
From that stalled point, which is exactly the one you described earlier with the V legs, I found that for myself the best way to finish the inversion is to put my legs on the pole in exactly the way that you and Empyrean describe. Then I can tilt my hips forward/upward some more, without rolling my torso up any further, to secure my leg grip; and then I can push myself off of the pole with my arms and arch my back so that I don't roll over my collar bone. I have also found that shoulder mounting directly into a Tammy (inverted thigh hold) is just as easy and comfortable as using the inverted crucifix; and that for myself, it is easier to get from a Tammy into whatever other position I would like to use than it is to transition out of a crucifix hold. Technically it is also possible to shoulder mount directly into a Gemini, Scorpio, or a Brass Monkey, but these can be very awkward feeling if you're not already comfortable with the regular shoulder mount into inverted crucifix or Tammy. I only shoulder mount to inverted crucifix if I plan to caterpillar right away, otherwise I shoulder mount directly to Tammy because it is easier for me to get into other positions from the Tammy leg position than from the crucifix leg position.
Just recently, also, I have begun shoulder mounting with the thumb of my right hand turned upward! This was very hard to get used to, but the coolest thing about this is that now that I'm a little more accustomed to it than before, I can shoulder mount directly into the twisted grip Aysha or straight edge, just by dropping my lower bracket (left hand for me) after I get my legs on the pole! I know it sounds like such a minor modification, but right now I'm really excited about what such a tiny modification has enabled me to do. But mind you, if I don't plan to Aysha right away, I still prefer to shoulder mount with both thumbs down. You could use the figurehead move to experiment with hand grips. Quite honestly I think the figurehead is a beautiful and underused move anyway and I love doing variations and exaggerations of that move. Its a great way to prep for a shoulder mount if you're strong enough to do the mount after holding that position for a few moments.