@13man18 That has been bothering me for some time as well. That very issue is like, the entire plot of a series on its own isn't it? One way I could see things going here I guess is with the confession stuff being a "mutual victory," but then the story enters the "disapproving father" boss fight. At this point, the two of them and maybe even the other cast members their age would be doing the whole victory/defeat/draw thing in regards to earning Prez and Kaguya her father's approval.
Another way I could see this advancing is that Prez has been an acceptable candidate all along for one reason or another, and the confession is the grand finale with that approval just being like "Oh yeah, that's cool. He was one of your potential marriage candidates anyway" making them both feel frustrated at the amount of time they wasted maneuvering against each other for the same goal under the same misconception that nothing real could come of it in the end.