.htaccess Simple Rewrite Question

G'Day,

I'm working on a site and I want to redirect users in the following fashion;

If they visit http://www.site.com/payment or http://site.com/payment

I want to redirect them to https://www.site.com/payment

I'm sure its possible I just don't know how to do it.

Also I have this code

Which should just get rid of the slash off the address name but it doesn't. It redirects the user to;

http://www.site.com/home/myusername/public_html/about/

Which is not correct. Does anyone know how to fix this?

Thank You!