I am not sure if you thought it was meant to "take' Ivermectin Pour On for Cattle.
That is not what is advised.
Just to be clear, many many people have used the Ivermectin Pour on for Cattle on their skin as a topical.
Many have also used Injectable or Oral Drench Ivermectin for cattle as an internal medication to swallow.
I have used it on myself and still am as a precaution. I have also used it on my 5kg dog.
Your fear is very understandable. I also felt that, we all do. The fear of developing a cancer from the meds. But for me, after years of torture, it was not worth living with the parasites.
There is no natural cure that will cure you. It's necessary to take the meds. I gave up trying to get them from a doctor so I settled on animal drugs that are researched well and made with care. If I had focused on only using human meds I would still be crawling years later.
Best wishes. I hope you can overcome your fear and trust yourself to do it with care. There is plenty of support on here. Don't put it off hoping for a miracle.