How to firm up modeling chocolate?
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That seems like way too much corn syrup. The recipe I use is 12oz chocolate and only 1/3c corn syrup. You're probably going to have to work the excess oil into. it. Knead the heck out of it to try to incorporate it as best you can-- it's gonna feel like an oil slick-- cover overnight with saran wrap and knead it again tomorrow. It may take a few days to get it the right consistency.
It's just going to take a while, could be overnight, could be a couple days. Modeling chocolate is one of those things that can't really be sped up. Hope it turns out well!