The Earth's atmosphere also consists mainly of nitrogen, although only 80% rather than 98%. However, I think oxygen and nitrogen have similar scattering properties, so the exact mix shouldn't matter much.
The sea-level pressure for your planet is about the same as airline cruising altitude on Earth. So if you crane your neck and look up you can see the deep sky blue color that people would see if they were orbiting the Sun.
The fact that the star is cooler means, I think, the the sky will be a bit darker, but not redder. The "redness" of the star really means that it is less blue than the Sun, and since it's light at the blue end of the spectrum that the air scatters, you will just get less of that.
But even "darker" might not be how it's perceived. The paleness of sky blue comes from the fact that there is a mix of light from other parts of the spectrum in there. If you dial that down while maintaining the same proportions, the eye will adjust and simply see a dimmer pale blue sky.
In general this is hard to get right. Before the Viking landers, a lot of popular science literature predicted the Martian sky to be dark, perhaps navy blue, because the atmosphere was so thin. But it's pink, or at least a butterscotch color. However, I think you should assume a variant of sky blue until proven otherwise.