short answer: I think you have yourself a nice little niche and if done well your writing could succeed. however your main character is much too childish for an older audience to relate to. If I were to be honest your story would probably be enjoyed by a younger audience; around grade 6-8 and even that's pushing it. That being said I don't feel like there are any other issues surrounding your story; spelling errors are to a minimum and you have a basic grasp of which direction you want to go in so it's all good in that department. That being said you still have issues that need to be addressed if you wish to bring this to an older audience.
long answer: here are some issues that are slowly making loose interest in your book...
~ one: Men don't really blush. Like at all. This bothers me because it's almost like you are writing a girl in a man's body. If you want to replace this emotion with something, then make it embarrassed irritation or anger. When men are embarrassed they output their emotions in a different way. Most of the time it's this weird defensive anger; men just don't really blush all that much. if you want to see an example of embarrassed anger go watch a prank video of some guy in a shower.
~ two: In one of the chapters (ch 13) the main was asked to take off his shirt. Afterwards when he was asked why he was embarrassed, he said that he was nothing compared to the other people around him; always the little kid. Even if it because he is in front of a girl there is something distinctly wrong with this as a male. Unless society has made the concept of taking off shirts the same for men as it is for women then there should be nothing wrong with it. I take no pride in my appearance (freckles covering my entire arms, face, legs and parts of my upper body not to mention the softness around my waist) but even i don't care about taking off my shirt. The same can be said for one of my friends who just so happens to be a scrawny little bugger with similar stature to your own main at around 5'7". Social edicate has made the idea that taking off a shirt on a really hot day (if you are a man that is) not really matter at all; the same society has also made it taboo for a woman to take of their shirts except for certain circumstance (swimming mainly). If you look at an amazon society it would simply be social norm for women to not care weather they were toppless or not.
~ three: In one of the chapters when he was just learning how to fight (ch 10) he was goaded into a fight and fell for the goading. This... could have been written much better. Before he was goaded into the fight he was asked by his wouldbe trainer to attack her. When he was asked why he wasn't attacking, he said that he didn't want to hurt her. She said "Try your best shot. You couldn't hurt me even if you wanted to" and of course he said "ill show you" only to land on his back immediately afterwards. This was done wrong on many levels. one: Where did he get his pride from suddenly; i thought he was timid little boy who always got his confidence ruined by his parents. I say little boy because he is definitely not acting like a 20 year old; he's edging more and more to the 10 year old territory the more i read about him. two: If he is intelligent and as old as you write him to be then he definitely wouldn't have said anything like "I'm worried I'll hurt you". He should have most definitely understood the reputation of Sorakine warriors. Anyone with that much prestige on the battlefield would have definitely been heard about (like Samurai warriors or Vikings). A suitable response from him would be something along the lines of: he looked aghast "Are you kidding me, you would beat me to an inch of my life." She looks down at him with a slight smirk "But pains the greatest teacher isn't it." he looks at her "You've got to be kidding me" he mutters then sighs "Alright, let's get this over with"... The main character was described as academic 20 year old who had a good head on his shoulders, but the way you've written him was more like a hot headed middle schooler surrounded by high schoolers. He could feel the pressure that they gave off and was suitably nervous but didn't quite realize that he was in way over his head and could not possibly beat them in a fight.
as i said before, with some polish you could definitely make your book shine, but right now you have some deep scratches that are ruining your book as a whole and need to be addressed. although two and three are situational and are not a trend throughout your story, I think back to how they were done and feel like they could have been done much better. another way of saying it; these two instances are the main things bringing down your story and need to be changed on order to bring out your stories true potential.
thank you for reading this and best wishes on writing