Hi,
Have you come across these Be StepWise videos? There are a whole series on this topic.
See this one called
"what to do when your step-child hates your guts"
https://studio.youtube.com/video/aqZfcjWLZp0/edit
You can find them in YouTube @bestepwise
Or this one called, "For when you have awful emotions towards your step-child", and one called "find out the early warning signs for step-parents", which talks about how things can be fine to begin with.
I hope they help, and all the best,
Alison