First of all your essay contains 138 words, while you must write at least 150 words.
I have just seen your advertisement
u can use this statement :"I am writing with reference to your advertisement...". In order to make the letter more realistic you can mention the name of the newspaper at which u have seen the advertisement.
I feel I am rightmatch
it would be my pleasure if Ito be awere part of it.
volunteer guide in tourist guides club of my university.
elaborate on this part. What is the name of your university? What was your responsibility? Talk more about your experience.
I am looking forward to your reply.
----> suggestion:"
I am eagerly waiting for your kind reply and really appreciate your time and concern