There are event you can predict on that even though it's not 💯 guaranteed that you're going to win, a level of certainty makes you think that you're surely going to win.
The downside of that feeling is that you might become over confident to use a big amount in the game since you're to a large extent certain that you're going to win.
Can we still say we are gambling if the event is something we are at least 90% sure that we are going to win?
Well depends on what you mean, I think...
If you mean by "if you're sure you're going to win" that you are making a fraud bet which has a certain outcome the other party is not aware of but you are, then that is not considered gambling but rather a scam.
A real bet in gambling is unpredictable. Sure, the probabilities can be easily calculated and based on them, the bet can be made but there is no 100% garanteed wins in betting (unless it is a unfair bet, as mentioned).