Wanted the stain a darker color & I'm guessing I left the (oil)stain on too long. All the stain doesn't seem to want to come off, still is wet. Can I fix it or do I start over?

You can try rubbing it with paint thinner but most of it has soaked in, depending on how old, dry, bare, the wood is and how long you left it on. Oak soaks up a lot quickly.