Since you are asking, you already KNOW it is too short!! Be a lady, not a tramp!! If you are uncomfortable sitting, or even thinking about it, it is too short!! What are you saying, wearing a short skirt? "I'm easy" or "I don't have any self-respect?" I'm old enough to be your father, I think, and I would NEVER let my daughter wear something that short!! Wear 'shorts' under it? Good idea, but if it is so short that you need to wear shorts, then it is too short!! Respect yourself, and dress like a lady!! You DON'T WANT the guys that want to see you in tiny skirts, because they are going to treat you like a toy, for their own joy!!
I'm sure your a nice person but people will assume bad things about you based on the way you look if you wear that outfit. Especially if you are young - guys will try to take advantage of you and might even rape you.
It doesn't seem too short... just be mindful of sitting down and getting back up again... and going up stairs and escalators at the mall... and getting in and out of cars... and windy weather conditions - makes me glad I'm not a girl at this point