Lucy Patel I'm sorry, I can't get in to your sessions. It is super hard to know what is going on to help you. If the Move Dart tool isn't working, you could try just using the Slash & Spread tool.
Slash & Spread in the manual
It is exactly the same process, but it doesn't figure out all the points of the dart by itself. I'm guessing there is some issue with the dart registration and that's where the problem is. Try the more manual method and I think you'll have better results. Also, it's very handy for you to understand the technique because you'll use it a ton. When I'm working with basic blocks and designing new patterns, I don't register the darts. I just manipulate the geometry with the Slash & Spread.