iPhone autocorrect keeps changing previous words

How do I prevent my iphone from changing previous words in the sentances I'm putting it. It seems that sometimes it likes to change previous words I typed in based on new words I'm adding, meaning I have to stop, move the frustrating little cursor back to the word, delete it, and type the word I wanted in again. I want the phone to believe the word I put in there was the correct one and to have no further control over it.

Here are my current keyboard settings: