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?
If you are 90% sure of winning, then this game is 10% gambling. If we are talking about sports betting, then this can be a trap. By the way, if this confidence is present in many bettors, then such a bet does not make sense. The gain will be negligible relative to the loss (which still has a chance). In general, it would be nice if you could give a specific example of what exactly we are discussing. Since the situation you described looks somewhat abstract.