I don't post here much but this one took my interest.
i don't think you did a thing wrong shadyhollow other than securing the services of an incompetant boob for a veterinarian. I also do my own sections and a few for neighbors as we live 200 miles from the nearest vet. Even the most complicated ones take less than 1 1/2 hours from start to finish.
It sounds to me that your vet incised too far forward and had to deal with the rumen in the way. Properly done, the incision in the uterus is made at the very bottom were the hind feet in a normal presentation are. This allows for the uterus to be sewn up while it is hanging outside of the cow. Two seams are sewn in the uterus, the first to seal the initial incision and the second is done outside the incision thus folding the first seam inward and reducing the chance of leakage from the uterus. I do a lot of them by myself. Did your vet do this?
Also use lots of pen, inside the peritoneum, over every seam and for ten days after the operation.
In my opinionated opinion, your inexperienced vet owes you a cow and should have the insurance to cover it.