If puckering is your problem, you may have too much tension on the presser foot. On vintage machines and sometimes on newer machines, you can "turn down" the pressure on the presser foot. On vintage machines, the knob is generally on the top of the machine straight above the foot. You just twist it - "righty tighty, lefty loosey".
(I have no clue how to handle it on electronic machines.)
Try that on your practice piece and see if it helps.
bkay