Can we still say we are gambling if the event is something we are at least 90% sure that we are going to win?
It is still gambling because there's a money involved.
Moreover, even you're too confident that your prediction is going to happen, in gambling, nothing is certain. It can go the way you didn't expect it to be. Confidence is not sufficient to win since there are many gamblers who do so yet they still lose. There's no such thing as sure, because if that's the case then probably many gamblers are already rich by now.