You have answered all the questions in the task, great job.
The text is logically organised, I can see paragraphs and some good linking devices (‘as a hobby, of course’). I would divide the first paragraph in two. Some linkers are not clear for me, too: ‘How you decided make along…’ – what is ‘How’ referring to?
You used a lot of nice vocabulary to talk about achievements (competitor, challenge, assume). There are quite a few mistakes with spelling (enjoinin, travell, trow etc.) Next time you can use a special programme to help you check your spelling, for example, Google Documents. With time, you will start to see these mistakes yourself.
You used a lot of complex sentences (I hope that…, If you read…) and the present perfect. That’s fantastic! Remember you should also use the future perfect in this letter (e.g., I hope you will have travelled a lot.)
Overall, this was a nice heartfelt letter, I enjoyed reading it. Next time, check your spelling befor handing the text in and remember to use the grammar that’s required in the task.