Corrected version of my first English homework assignment

This week our English teacher Fiona returned our first piece of homework to us and let me tell you, it was a shocking experience for me... ;)
I was always a pretty good Student and to be honest,for an English homework or test I´m not used to being graded with anything worse than a B. For our first English homework at university we had to write a letter to our teacher Fiona, telling her about us as language learners and I got a D. When I saw what mistakes I had made, I couldn´t believe how stupid I am sometimes. On the one hand I was so shocked about my terrible grade, but on the other hand I´m really glad that Fiona is so strict when it comes to correcting homework assignments, because this is the only way I can learn and improve my English skills. If everything I write would be perfect already, there wouldn´t be a point of studying at university...
Anyway, this week our homework task is to correct and rewrite our letter and make it the best we can. Here´s the corrected version of mine:

Dear Fiona,

I chose English and Spanish for my studies at university because I love these two languages. I had to take English at school for eight years. Spanish I only had for three years, which now gives me a little bit of trouble, because my language skills in Spanish are not that good. When it comes to learning languages, it was always easy for me to learn and remember vocabulary, but to learn about grammar usually gave me trouble. How to form different tenses and when to use what tense was always hard for me to figure out. To help me become confident about the different tenses and to get a wider range of vocabulary, I like to read books or watch movies in my foreign languages.

When I was fifteen I spent one year in Aspen, Colorado, as an exchange student, which was a great personal experience for me and a very good opportunity for me to improve my English skills. I lived with three different American host families throughout that year and I attended Aspen High School, so I really had to speak English all day long.

From February 2012 until March 2013, I was an au pair in New York, which again helped me improve my language skills. Another great thing was that during that year I had to get six credits from an American university or college. Thankfully, the au pair organization makes the host families pay for that, because everybody knows how expensive American colleges are. I attended Westchester Community college for three months, where I participated in an English class. I hope you got to know me a little better and I could give you a good impression of my English skills.

Yours,
Verena

Again, I can´t believe what stupid mistakes I´ve made, writing this homework, especially mistakes that are part of the Major No-Nos list. I know that you have to write out numbers, that are smaller than twelve and still I didn´t do that for some reason. I also know not to use "especially" at the beginning of a sentence, but when I went through my homework just now, I saw that I did. Some other things I just wasn´t sure about, for example how to correctly write "au pair" (do you write it with a capital A and P or not...). Now I know and I´m definitely not gonna make the same mistakes again.
Another important thing is to read through your homework after you printed it, to make sure there are no spelling mistakes and that the formatting is correct.
I will keep all of these things in mind, go through the Major NoNos list again and then hopefully not make that many mistakes in the future and get a better grade on my next English homework... ;)