People justify a yuri ending and all that, but what if we'll just get an "everyday" ending. Matsuri will visit her for the last time, with the usual shenanigans, a big smile, and a "the end". It won't deny nor prove anything.
Then again I might be a bit unfair. From what I experienced reading some comments, if there's no sex scene, the yuri is not.
Who cares? (Well, I know some people do, but I surely don't.)
Look, this series started off like a 4-koma with a slightly wacky premise, with Matsuri as the genki-girl boke and Miss Sunflower as the stoical tsukkomi. Matsuri's initial "I love you!"s seemed to come out of nowhere as a bizarre personal quirk, and the gap between their ages and their personality types suggested that there was no plausible room for any kind of real romantic development.
But it has slowly and gradually turned into something rather different, something more serious and with higher emotional stakes. We learned that their ages aren't all that far apart, that Matsuri is considerably more thoughtful, diligent, and mature than she once seemed, and most importantly of all, the focus of the series has turned to the emotional development of Miss Sunflower as she allows herself to open up her previously closed-off feelings, almost entirely because of Matsuri.
To me this series has done a great job of slowly developing its cast of characters and of mixing gentle comedy with scenes of meaningful emotional growth. Basically, it's consistently been extremely thoughtful and well-written, and as long as it keeps being that I expect I'll be fine with wherever the author decides to take it.