Je deéteste mon l'école

"mon l'école" is impossible just like "my the school" would be impossible in English, same reason

La tetedirection due mon l'école ne travaille pas proprecorrectement.

"tête" can mean "direction" only in some specific situations, here you'd say "la direction"
"pas proprement" would mean they would spread dirt or mud all around
"travail" is only a noun

J'obtenai trop des devoirs.

"obtenir" wouldn't be used in this case. "Ils nous donnent trop de devoirs" ("we're given too much homework") would work though
Simple adverbs of quantity = de (without article) => beaucoup DE devoirs, trop DE devoirs, peu DE devoirs, plus/moins DE devoirs

Il y a les projets due groupe, le français, les affaires, et la CAS (creCréativité, aActivité et sService).

"les projets DU [de+le] groupe" would refer to the projects of one particular definite group
CAS would be given an article, if it's a school subject; since it's an acronym, all words composing it would be capitalized

Toutes ces choses prendent mesempiètent sur mon temps libre.

Feminine plural agreement with "choses" => touTES

These things take your time, but by definition it isn't free since you're busy with school. You can however say "empiètent sur mon temps libre" (lit. "infringe upon, overrun")

You're talking about time in general here, the time going by, and this one is uncountable singular => MON temps

Alors, je n'ai pas lesde temps pour moi(-même).

Absolute negation = pas de (without article) => pas DE temps
Would be more natural to drop the "même"

Je déteste vraiment deteste ma [principale/proviseure ?] parce que 'elle me réprimande toujours.

In a simple tense, there is no adverb between the subject and the verb

The head of a middle school ("collège") is called "un principal" but the head of a high school ("lycée") is rather "un proviseur", at least in France

que+vowel => qu'

"réprimander" would have an object here => me réprimande

Pourquoi ?

Space before and after ! ? ; : « » %

Parce que je toujours change mes sujetselon elle, je change toujours de matières...

"selon elle" to clarify the statement is her opinion only
"changer de" makes it clear you meant "to go for something else" and not "modify"
a school subject = une matière scolaire

Je ne demande jamais à en changer mes sujets!

en = de matière (it avoids repetitions)

Jamais1 ! Elle me réprimande toujours pour pasans raisons.

"for no reason" is an English syntax that can't be translated literally

CeluiEn ce moment, elle réprimande ma soueœur parce que 'elle déemande pour plus de classeours de la matheématiques, comme elle a tempdes difficileultés.

"demander" is directly transitive (demander quelque chose)

"mathématiques" is always (feminine) plural in French

"class" in the sense of "lesson" is "cours"; 90% of the time "une classe" is a group of pupils or a classroom

Same issue as above, "to have a hard time" is an English idiom that doesn't translate literally
to have a hard time = avoir de la peine, peiner, avoir des difficultés, galérer (colloquial), avoir du mal (the translations depend on the context)

Elle lui a dit, " : « Qui êtest-vous pour me dire comment je dois managérer/diriger cette l'école." ? »

French quotation marks => « »
I supposed you meant "who are you to tell me how I should manage this school?" (this is what I corrected)
"manager" is an anglicism mostly used in the corporate world, the French equivalents being "gérer" or in this case, "diriger"
"cette l'école" isn't possible, it would be like saying "this the school" in English

Nous avons seulement demandons pour plus de classe gentilementgentiment demandé plus de cours !

So far I understand, you did this in the past => nous avons demandé
If you're still asking for some more classes, you can use the present tense

Cependant, j'adore mona professeure due français, même si elle donne trop des devoirs.

"professeure" is pretty much always used in the feminine, when a female is teaching
Common colloquial abbreviation => ma prof

Merci pour m'aidezde m'avoir aidé(e) !

merci DE faire quelque chose ("pour" is used with nouns)
Here with past infinitives, since you're thanking us for a past action => merci DE m'avoir aidé(e)
"aidéE", if you're a female, "aidé" if you're a male