While this lesson may be in the present tense section, as I understand it, Spanish is not as strict with its tenses as other languages might be. Below is a chart I pasted for someone else in another discussion thread. You may find it useful, so I'm pasting it here again:
Most present tense verb forms have several equivalents in English. For example, the form hablo may be translated in numerous ways:
You will notice, if you visit the actual web page, that I added a little flair to it and corrected a typo. Other than that, it should be identical. The web page the chart above came from is below:
So, if duolingo doesn't accept "you are not running" as an alternative, it is a bit surprising. Then again, as elissaf1 has pointed out, this is from the
section of this course. Though you may be tested comprehensively when you do strengthening exercises, duolingo tends to stick pretty closely to the lesson topic within the lesson itself.
Hope that helps you in the future.
P.S. I notice that you are now at a Level 14 in Spanish (¡Enhorabuena!) so you may be well beyond anything I wrote in this post. If so, I hope it helps someone else.