How to shade area between two verticle lines

[Bonnie88]

Hi,
I am trying to shade an area on a line graph between a data point in the 30th and a data point in 80 percentile of a set of data.
I have managed to get the area highlighted, but the shaded edges are on an angle. I want the edges of the shading to be straight and directly on the correct X-Axis point.
Do you have any idea why the data might be doing this? Below is a picture is what I'm trying to explain (hopefully picture works).
Thanks!
Bonnie

excel.png

[Crooza]

Can you post your actual worksheet?

And welcome to the forum