My poor pronounciation,What to do?

learn the sounds that starting letters and finishing letters make and ensure you make the sounds properly.

You may even like to eggagerate the sound at first.

A good dictionary usually lists the vowel tones which indicate how to pronounce a word. Since I don't know Mandarin, it's impossible to point out what YOU in specific should pay attention to, so your best bet is to use something like that. Perhaps listen to internet radio broadcasts, if you are allowed to.

Exaggerate I made a spelling mistake.

Since your written English is good, I think you should listen to books on tape or cd's. You can find used tapes on Ebay or from Amazon.com. A well read book should be sound clear and have correct pronunciation. You might want to start with children's stories for simple vocabulary.