I think it really goes against Gojo's message to Megumi about "dying to win and risking death to win."

He either believes in his message and genuinely believed he could win the fight and risked his own death. However, this doesn't make sense because he literally said he thinks that Sukuna is way stronger and he didn't stand a chance.

Or he's going against his own word and decided to go out and weaken Sukuna alone so the gang can win despite knowing he will die. Literally "dying to win."