We get two variations per listing. If you want to make one for size and put your own sizing in, scroll to the bottom of the variation and choose your own heading. Then add your own options.
If you are using the preset sizes in the Attributes area of the listing form then you need to click on "Offer more than one ->" (underneath the Choose a scale box). It will open a popup dialogue, allowing you to select multiple sizes.
You can also define your own variations and options:
