I have found that following the swing line is just a simple 7-1 swing and you will get a slight fade or draw, its nothing really extreme unless you want to swing 8-2 or even more. Yes its hard to perfectly replicate that line but the swing plane is only little bit off a north/south swing. Just keep practicing and it should get easier. If you get the historic edition then you will have the practice range to tinker with it as much as you want.
The key, just like real golf, is to not to swing too hard because that's when everything can go bonkers. It's all about tempo. Take an easy swing back and forth until it becomes second nature and when you get comfortable increase your speed but you still don't need to flick it really hard to get good distance. This swing is meant to be measured as well as accurate. Flicking it hard forward will hurt your tempo and makes it more difficult to have a diagonal straight line and the devs have stated that tempo is a factor with accuracy, its less forgiving when your tempo is bad.