Force feeding your cat anything when it isn't medically necessary is never a good idea. There are other ways to give your cat a nice coat without force feeding vegetable oil, usually by increasing the quality of the food you are feeding.
I really do think you should give your vet a call and explain to them what happened and how your cat is acting.
2 ounces is a LOT of oil. I would get him to the vet asap. Your kitty is probably going to have serious digestive issues for a while and consulting a vet needs to be done. Diarrhea and vomiting can quickly result in dehydration which could also quickly kill a kitten.
As stated above, upping the quality of food can help with coat or SMALL amounts of fish oil *once or twice a week* can help.
If he's only 3 months old he still has his "kitten" fur. As they mature, the fur will change also. And some cats just don't have "sleek" looking fur. Out of my five, Poppy is the only one whose coat looks sleek and shiny. The others, not so much. Kind of like people.