Just two things that she didn't put in her corrections. How many meets do you have per week? 2? You do the steeplechase, right?

Diet organization

Since I'm studying a degree in nutrition and dietetics and i'm a really sporty active/athletic person, I'm usually concerned about what I eat, regarding to the amounts of what I eat, it's quality and the combinations of food I choose, that's why I usually read the labels before eating something and be very careful with the timing of eating.

That's not always easy, because I have a very charged busy/tight schedule due to the university, the workouts and the languages classes, so I usually carry some food in my backpack so that I can eat someting between classes instead of getting more and more hungry.
However, I can't carry milk in my backpack, I've tried some times, but the bottle has broken, pouring the milk on my books. That's a problem when I have to train early, because I can't have milk for breakfast within the previous hour to the workout.

So, if I want to give my best in workouts, competitions and classes, I must be very accurate in organizing my diet

Diet Organization  (With titles, capitalize all nouns...actually almost everything except prepositions like of, by, for, of, with, etc.) 

Since I'm studying for a degree in nutrition and dietetics and I'm a really sporty person, I'm usually concerned about what I eat, regarding to the amounts of what I eat, it's quality and the combinations of foods I choose.  That's why I usually read the labels before eating something and be am very careful with the timing of eating.

That's not always easy, because I have a very charged schedule, due to the my university studies (or "studies at my university"), the workouts and the languages classes, so I usually carry some food in my backpack so that I can eat something between classes instead of getting more and more hungry.
However, I can't carry milk in my backpack.  I've tried, some at times, but the bottle has broken, pouring the milk on my books. That's a problem when I have to catch a train early, because I can't have milk for breakfast or within the previous hour to the a (or "my") workout.

So, if I want to give my best in workouts, competitions and classes, I must be very accurate careful about in organizing my diet.  (Or, you could say, "I must organize my diet very accurately" though most English speakers would use the word "carefully" in this context.)