I'm not obliging you to do this, but it's just a thing to know. In Europe, you always give girls an odd number of roses because even is bad. It's extra knowledge you can use to your advantage, if she asks or if others ask, they would be intrigued, it's a DHV. Now moving on..in my opinion it would be better to give her 5 roses (4 white and 1 red in the middle or vice versa). If you get the big, meaty roses, it'll look like a bouquet even though it's 5 roses. (I've legitimately done this on a Valentine's Day before by the way. The roses had some green strands and glitter on them, it was epic.) I always focus on originality, so if you take my idea, it will definitely work in your favor.
Now on the note write:
If you held five roses up into a mirror, you'd be looking at six of the most beautiful things in the world (her name).
Love/sincerely,
-Your name
That's it. Simple, cute, original. Nothing long or going on about your feelings. And it's Valentine's Day, who gives a shit if you say, "In the world"..everyone exaggerates on Valentine's Day.