A few things to note as webflow's checkbox has its quirks:

1) Raise the z-index of the Checkbox Text to 10+ to edit in the designer. You will have to set it back to auto before publishing (if you know of a workaround, please let me know!!)
2) Make sure you're editing both the Checkbox Text and the Checkbox settings to reflect the text
3) I've hidden the webflow-generated checkbox text and used a standard text element in its place