Make sure that the spot you choose to start from on the approach allows you to hit your mark. For example, if you're playing a straight "down-and-in" shot up the second arrow (10th board), your bowling shoulder should be in line with the second arrow. If you're right-handed, that means the right edge of your right
shoe should be somewhere around the 14th board. (Most coaches seem to teach using the inner side of your sliding
shoe, but I find it easier to use the non-sliding
shoe as my reference.)
If you begin your approach in the wrong spot, it may be physically impossible for you to hit the mark you're aiming for, without turning your body this way or that at the foul line.
Then try to push the ball away from you in a straight line, and let it swing freely. If you're lined up properly, and you're missing your mark to the same side by about the same amount (two boards to the inside, for example), then try focussing on the board the same distance to the other side (two boards to the outside, in my example).
Hope this helps.