well, in the context of quality assurance / process improvement programs I've seen diagrams that display regression lines, and then show the uncertainty by drawing a small normal distribution curve centered over the line, and indicating the standard deviation with a label.
Can you picture that?
Here's an example I pulled out quickly, but you can probably find better examples:
for HaxorNubcake
If you can't read this scan then PM your e-mail address to me & I'll send it to you.
So for your
regression line you could show the uncertainty / variability with a bell curve straddling over the line. Label it with its standard deviation.
For your
slope, you could show uncertainty / variability by maybe drawing 2 regression lines, one being the min slope & the other being the max slope. You could designate the uncsrtainty by drawing a little normal distribution curve sideways along the y-axis between their y intercepts, and label it with its standard deviation.
Or for your slope, here's another way to show the uncertainty:
since slope is simply the 1st derivative, you could take the 1st derivative of your regression line, and draw the result as a line, then straddle a normal distribution curve over it to show the uncertainty of the slope.
(In actuality the uncertainty may not follow a normal distribution, but I'd think it's fair to assume it is for purposes of your exercise. You could maybe put this fact in a footnote.)
"How" to display data is a large subject, and if you look in your school library you'll find entire books dedicated just to How to display data. Just ask any business or engineering grad student, or your research librarian, about how to do it.