Your username will be public.
Consider using an anonymous username, not your real name.
If you use your real name as your username, your real name will not be private and will not be able to be made private later.
However, this message is poorly displayed and flows quite badly with the rest of the page. The hardcoded and user-defined portions of the page are visually very different, which is off-putting. Improving the visual design would make the signup process smoother and more pleasant.
Please design Special:CreateAccount to allow local communities to display warnings that are visually well displayed. Also, consider adopting default text similar to the English Wikipedia privacy text.