When u try and use an american accent, make sure u follow their intonation part as well. American intonation is simple. The kep is to stress only on the most imp words in the sentence. Those are the verb or the noun.
Ex: DAVID called me.
he CALLED me.(CAps stresed)
Stretch ur vowel sounds (unlike the british pornunciation where they are more or less contricted)
Be sure about the plosive sounds as well.
Gosh , This looks like a feedback i am giving to an agent!!!