You have already used the right word - glance. Set Power, Attitude and then Trim. Only when you have done this should you 'glance' at the instruments. Look out again and assimilate the information you have just absorbed whilst confirming you still have the selected attitude and are in trim. Glance at the instruments a second time and then back out again. What has changed? If you have gained/lost altitude, select a new attitude by adjusting the position of the horizon, wait a few seconds, then trim. Wait. Glance at the instruments and back out. Wait. Glance at instruments again then back out. What has changed? Have you achieved what you want to achieve (level flight)?
A couple of other things:
Never chase the instruments.
If your wings are level but a point on/near the horizon is moving L/R, then you are not in balance. Check the ball.
Listen. If the engine noise is changing and you haven't adjusted the throttle you must be either accelerating or decelerating (think car going up/down hill with a constant pedal position).
Enjoy. These early lessons 4-9 (you're talking about 6) are imperative as they form the fundamental building blocks. Don't rush, or allow yourself to be rushed, through them.