Even if it was a perfect fit, Cinderella's slipper still slipped off because it's supposed to slip off. Not just for the sake of the plot, but because it isn't called a "SLIP-per" for nothing. I'm not done. If you ask me, Cinderella's slippers look less like slippers and more like high heels. In fact, now that I think about it, out of all the shoes she could've worn, she chose GLASS slippers?! Knowing glass, it's not only very slippery, which is another reason on why it slipped off, but it's also pretty fragile, so it's not just uncomfortable, but also VERY F*CKING DANGEROUS! She's putting her feet at RISK of having glass shards stuck in them! Unless the glass is heavily tampered, if she stubbed her foot on ANYTHING, her slippers would shatter, sharp glass shards would end up in her feet, she can't go to a hospital because those don't even EXIST in her timeline, she would lose so much blood, AND THEN SHE'S GONNA DIE! He's still out of line, but he's right again.
