I am not sure why the system is not letting you create forum posts – have not had anyone complain about it so far. Let me know if you still have trouble. Probably you can try creating a new user id and see if it helps at all.
To center the pricing table, just wrap the whole code within [segment] shortcode. Pls see examples of this in the sample code and explanation of this shortcode in documentation. I also did some explanation of this here –