Improving one's recitation of the Qur'an

I am slowly learning tajweed and when I read the Qur'aan, I feel that where I need to pull the word for a few seconds and I don't pull long enough, or pull too long then I feel that I have to reread the word, or if I don't recite a word properly with tajweed or if I feel that I didn't read a word with tajweed then I have to reread the word. Sometime I feel that it is Shaytaan that is trying to confuse me and frustrate me. So I wanted to know that if I don't pull a word for the correct time or if I don't read a word with the correct tajweed then is it necessary to reread the word?