I saw where children are tough using grid paper first and then they draw lines on regular paper and sew over those JUST to get the practice.
Don't give up. Maybe your strips are not printed straight. (Not all stripes are created equal) Are you sitting square to your machine? Is your foot pedal close or do you have to reach? Do you go too fast?
Do you have a guide that helps you keep the seam allowance consistent? I use the 1/4" foot, others use tape or mole-skin pads as guides.