Выделяю ошибки красный, а стилистику синим.

I am afraid to fly.

Hmm..No, I'm not afraid to fly, but I am afraid of crashing! I like to travel a lot, but I prefer trains to planes.  I have flown [1] by plane 4 times.  I have traveled [1] to Croatia and to the Czech Republic. When I flew to Croatia, there was a very beautiful view from the window. It wasn't a terrible experience for me even though [3] it was my first flight. However when I flew out of the Czech Republic, it was a winter [?? 4], and I didn't see anything out the window. The plane shook, and I started crying. The stewardess came over to me, and said, "Oh, as lovely! [?? 5 ]  Do you want a sedative?" I said, "No, thanks." And I began to watch animated cartoons. Since then, I have been thinking [6] what my next flight will be.....)
Please, correct my note.
Mary.

[1]  The "present perfect" tense is good to use when mentioning an important experience in your life, especially one which is still important to you.

[2]  traveled (Amer.Eng.)   travelled (Brit.Eng.)

[3]  Variant: ... for me despite the fact it was my first flight.

[4]  Do you really mean it was "winter"?  Or do you mean as Cedric suggests, that there was a snowstorm?

[5]  "Oh, as lovely!"  is not understandable.  Are you trying to translate, "так красиво"??  Do you mean "so lovely"??  What is "as/so lovely"??

[6]  Use the "present perfect" tense ("I have thought") or the "present perfect continuous" tense ("I have been thinking") when an action began in the past and has continued until the present time.  Using the "present perfect continuous" tense emphasizes the duration and the process.

I am afraid to fly.

Hmm..No, I'm not afraid to fly, but I am afraid to fall! I like to travel a lot, but i prefer to use the train more over airplanes. I flew by plane 4 times, I travelled to Croatia and to the Czech Republic. While I in was to Croatia, there was very beautiful view from the window. The flight wasn't terrible for me despite it was my first time on a plane. However when I flew from the Czech Republic, there was a snowstorm and i didn't see anything in the window. The plane shook and I started crying. The stewardess came to me and told: "oh, as lovely! You want a sedative?" I told: "No, thanks!" And I began to watch animated cartoons. Since then I think what will be my next flight...)
Please, correct my note.
Mary.