"High school friends Mark and Joel have their lives uprooted when Joel discovers that his late mother was actually a princess who ran away from another world.
Upon the death of the last remaining heir to the Obdresti throne and with the King old and infirm, Joel is asked to return that world and claim the crown he will inherit through his mother. Before that has has to graduate high school, figure out his place in a new world, find out what lead his mother to flee in the first place, and avoid running into what or who has been killing off the royal family."
Honestly, I find this part interesting. However...
"Mark, a nerdy kid without many friends, must choose whether or not to follow his friend to a new high school in a new world. It can’t be worse than NYC in the early 1990s, can it?"
...this part is quite the mood-killer for me. I mean, we all know that Mark will follow his friend to the isekai abyss, or the story would end there. I suggest you rephrase this.
As for the other aspects...
Cover Art: Actually, ScribbleHub is a place for western fantasy/western 'isekai' stories (OELN). It's not an exaggeration if I state that you use the 'waifu' cover, since it does attract readers to your work.
Content: I got no problems so far. It's a pretty solid narrative.
Other suggestions: Don't be discouraged by the lack of readers at first. As I said before, SH is a place with a lot of 'isekai' stories, so your work would be a drop in the ocean. However, if you keep on updating on a regular basis, it would soon gain traction, and hopefully, it'll get famous.
Hope this helps you!