As a female myself, I do have a few critiques of this piece. 
First off, I do think you seem to overlook one of the main purposes of a scrupulous dress code, and that is to enforce the idea that there is a place and a time to dress a certain way. Once you get to the workforce, dress codes are ubiquitous, therefore, it makes sense for schools to expect a certain level of decorum in the way their students dress. Obviously, I'd agree that the code ought to be enforced equally among both sexes, I just think boys/ men seem to run into less trouble with a dress code because most men's style seems to be more conservative anyway.
Second, you seem to imply that men or people in generel possess the ability to control their thoughts or consciousness. This just is not true. Sexual thoughts in particular are controlled by the amygdala of the limbic system, one of the most primitive parts of the brain. Therefore, we possess very little control our these thoughts. To imply that it is the boy's fault for having sexual thoughts is just psychologically and cognitively incorrect, very puritan, and destructive for a young boy's esteem as well. Obviously, yes, behavior can be controlled and if a boy chooses to act on these thoughts, that is completely his fault. Therefore, to expect a level of decorum and modesty from both men and women among a school dress code is important. After all, school is to learn. This is one of the reasons why many dress codes prevent religious/ political symbols to be worn because it is not the time or place to wear such. 
Third, you are obviously very passionate. But before you published this, I would advise looking over your spelling and grammar. It takes away from your ethos as a writer. Same for all the obscenities, a lot of readers may see it as sophomoric. Good work though! 

And, anyway, the fact that girls get blamed for the problems of the ####### boys of my school is total bull####. It's the worst. It's not our fault that boys misbehave! We can't control them!

How can I help change my school's dress code? Can you give me advice? Our dress code is ridiculously sexist, because girls aren't even allowed to wear flip flops(while boys can), tanks(again, WHILE BOYS CAN), and leggings with shirts that cover our backside! Ugh, someone needs to change it!

I agree with both parts. I went to a Catholic high school that had a uniform and the bullshit girls endured because of that was ridiculous. I also went to Catholic elementary schools that enforced sexist dress codes so from my experience the over sexualization and shaming of young girls comes largely from religious culture. They teach that women are responsible for not "making their brothers fall into sin." This allows people to blame girls and women if they get sexually harassed or assaulted. It's a way for men to control and subjugate women and they start young. Dress codes are reasonable enough but not when there's ridiculous double standards. 

I red both parts and I must say, that I agree, but only partially. Dress code can be sometimes too much. I see nothing bad in showing some collar bone or shoulder, wearing shorts or a skirt that isn't at a nun-length. However, and this is a big one, there is a limit how short is too short and how deep too deep of  a cleavage is. In my country we have no specific dress code - t-shirt, skirt, tank-top - everything goes. Still, when we were in 5/6 grade there was the high-fashion of  belt-skirts (basically barely covering your behind).  I have to say, I found it quite shameful, since it made one look really like a paid night butterfly (if you catch my drift). Still, it was somewhat tolerated. Now, call me an old hag, but I don't find it appropriate for someone to wear a shirt where your boobs are about to fall out, or a skirt that is virtually absent. As for sun glasses - this was the only thing that was taboo for us at school... o.k., that and running shirtless in the school premises.  And I support it. Showing your eyes during a conversation, and a class is supposed to be a form of conversation between teacher and students, is a show of respect. And being a boy and running shirtless... well as far as I could remember my school days, all of us girls had quite the raging hormones and were quite distracted by the occasional shirt getting accidentally lost during PE...

All in all, too strict dress code is stupid and laughable. But as much as clothes are a form of expressing yourself, school is not a fashion show. I find it sad if someone can not find another way to express themselves other than wearing something that barely passes as body-coverage.