There is a big difference when you jump from a disposable straight razor to a regular straight razor and even more when that razor is a 6/8 blade or wider. With a disposable, you can get away with a much more open angle than you can with the real straight. With a 6/8 blade the tendency is to bend the wrist back opening up the blade angle to 45 degrees or more. That causes all kinds of problems including scraping and pulling. Jumping tends to be more a problem with lather or tentative shaving. Make sure you keep the razor vertical when shaving. Think in terms of the razor spine being only one width off the face. Try this just from the sideburn to the jaw on one side till you get it and then move on. You will have to compensate more on the chin and other tough places just as you learned to do with the disposable.
Have fun.