The acting done by the leads is quite good (real emotion, great chemistry, etc.) - but that's what I would expect from Natasha Little, Douglas Hodge, and Colin Salmon. The story on the other hand...
You know the cringy prom trope? Where the handsome jock is dared to take the nerdy girl to prom and make her prom queen, and throughout this journey he falls in love with her? I feel as though this plot is dangerously similar to that. Frankly, this story seems like something out of a 13 year old's fanfiction.
In short: the story is ridiculous, improbable, and convenient.
But, if you're looking for a lighthearted, pastel, occasionally humorous movie with great performances from the leads, you've certainly found an option.