That looks like oil, from cooking, that was polymerized to your pan. The idea behind seasoning a cast iron pan is to have a polymerized layer of oil evenly coating the interior of your pan. From your description, it doesn't sound like you've seasoned your pan, or maybe, as pointed out in the comments, you did not complete the seasoning. While a well-seasoned cast iron pan can take occasional soap and water cleaning, you probably want to treat a newly seasoned cast iron pan a little differently when cleaning, avoiding soap and water, and just using salt, wiping out, and heating up. If you can remove it, go ahead, then resume the seasoning process. I'm guessing this will be fairly difficult to accomplish. I would continue to season, use, and avoid soap and water for a while.