It's nice to think to keep the Ambassador busy, but you could also have made this reservation on the website and selected whether to use the cert or only points. At least then you'd have seen what was coming before confirming.

In fact I suspect you could open up the current reservation now, click the amend button and then adjust how the payments are made with points, certs or cash. That may or may not offer some opportunity for a saving, particularly with points prices changing all the time now.