Remember when you turn the blade cannot turn a quickly as you can turn the board. You have to wait a fraction of a second or maybe it is a second, for the bladed to "catch-up". Go to the line you want to turn at, add slight back pressure so you stop cutting forward, turn the board and hesitate long enough for the blade to catch-up and then proceed forward.
Another thing I do if I want real sharp pointed turns, and I am cutting next to a waist area, is scroll to the line to stop, back the blade up and cut around so I can cut in from the other direction, to make a very sharp point or 90°. You can cut where ever you want in the waste area, it is not going to be part of the picture. I do the same on outside points that I want to be real sharp, cut past the turn point loop around in the waste area and come back to the point from another direction.
If you can, try to figure out my picture below on how I would get "sharp" corners. #1 I would scroll to the spot where I want to make the sharp turn, back up and cut past that point to the horizontal l line and continue. I would do that on all places that need a sharp clean point in this one cut. After getting back to my starting point, remove the waste piece than go back and finish cutting the sharp point coming from the other direction....
On the outside cut #2 I cut past the point loop around and come back from another direction to cut the clean point.
Hope this is some what understandable. I am not good at explaining and graphics. But remember, you object it to make clean sharp points and corners, you do not have to follow the line from start to finish, you can cut any direction you want in the waste area to accomplish you goal....