Unlike exotic vets, Betadine is neither expensive nor far away. You'll find it in the first-aid section of your local drugstore. That little bit of effort and expense will go a long way toward helping your snake pull through.
No sense in kicking yourself over your mistakes. We've all made them. Learn from them and move on. A neurological condition is challenging for even experienced keepers to handle. So, if you find you can't handle it, there is no shame in surrendering him to someone who can.