@faye—one trick my brother used is to put the cast iron thing on a really really hot grill outside, wait until it’s really hot, then just keep dumping oil in small amounts on it*, then let that burn off. It’s pretty dangerous (the oil will probably catch fire at some point), but it’s in a grill, so you can just let it burn out. This gets a LOT of carbon into the cast iron skillet, closing up a lot of the more open pores.
Let it cool, and then try seasoning it again. You might get lucky!
*—This is the dangerous part. I recommend using something like a shotglass held with tongs to get the oil into the pan. It’s going to flare up, and you don’t want your eyebrows anywhere near it, nor do you want a bottle of oil over the grill when you do this.