Test out the straightness of your stoke. To help you with the aiming, use the head string and the point on on table to line up the shot. It is also a good idea to use a striped ball instead of the cue-ball.
If you are within 1-3 inches of your cue, smile. Unless you are using brand new cloth stretched tight it is very difficult to have the cue-ball come perfectly back consistently. The rail bumper could even through the shot off.
Positioning your target ball with the stripe riding vertical and stroking straight through it you will notice if the shot isn’t straight because the line will wave instead of run smoothly.