A wing can look perfectly straight while you pull the eyelid sideways, then change direction as soon as you release it. Before adding more product, look at the shape in the position in which other people will usually see it: eyes open, face relaxed, looking ahead.
This is a small placement exercise, not a rule that every eye needs the same angle or length. Different folds and preferences call for different shapes.
Map a short ending before drawing a thick line
Sit where the mirror is easy to see without lifting your chin dramatically. Rest your working arm if that makes the movement steadier. With a suitable eye-area product, make a small mark where you would like the wing to end, keeping the applicator away from the eye itself.
Start shorter than your intended final result. It is easier to extend a modest shape than to remove a large dark triangle. Look straight ahead again before connecting the mark to the outer lash line.
Check the visible shape, not the closed-lid drawing
Fill a little at a time and pause with both eyes open. If a crease interrupts the line, adjust the visible outline in that relaxed position rather than stretching the skin until the drawing looks simple.
You do not need to force both sides into identical measurements. Compare their overall direction and visual weight from an ordinary viewing distance. Repeatedly thickening one side to match the other can turn a small correction into a much heavier look.
For practice, try only the outer wing before committing to a complete makeup routine. Take a break between attempts and remove product gently using an appropriate remover and its instructions. Do not scrape at the skin or keep applying a product that irritates.
Once you like the result, note the mirror height and the first small mark that helped. A familiar starting position is more repeatable than copying a dramatic close-up from a different face. The aim is a comfortable shape you enjoy wearing, including when you blink, smile and stop posing for the mirror.