Hi Carmen. I started conversing with a friend who speaks Spanish. I'm learning Spanish and I'm a native English speaker. We have been using this technique ; He reads a sentence in Spanish, then I repeat the same sentence in Spanish - and he corrects any pronunciation mistakes I make. Then I read the same sentence in English and he repeats the sentence in English etc..
If you can read English well enough, then this technique will work for you to improve your English pronunciation. Let me know if you want to try. I'm not learning Mandarin, but I could help you anyway.