Where should I put my number?

I’m so glad you asked!!

Your number should be exactly halfway between the level of the bottom of your leotard’s armhole and the level of the top of your leotard’s leg height.
This will give you a balanced look, rather than being top or bottom heavy.
It should NEVER be lower than your naval and ensure that it is straight before you march out!
There’s a trend to put them lower and lower but it’s not a good look and, if you have any hip movement at all when you march, it will just accentuate this.