Dont worry too much, I had one a few weeks ago and it didnt hurt, the procedure anyway, as long as route canal treatment is what you need itll be fine.
Ill level with you, its not fun and the worst part is if they inject you directly on the nerve which stings like a b***h, only for a split second tho so dont worry its like a pin prick right on a nerve but theres no after pain.
What happened to me after my route canal is they had to pull the tooth cause the route canal didnt save the tooth and it was hurting pretty bad, but now after the route canal and pulling of the tooth the one behind the pulled tooth is hurting, I feel like my dentist created more work for himself and is still doing so which is why im changing my dentist.
I used to be a mechanic I know how trades like this work, you create your own work ;)
the best advice I can give you is get a second opinion before you do anything, otherwise youll end up like me, a missing tooth and another one which feels like it needs to be pulled too......