Does a Slanted Cast = a Slanted Nose?

No. The slanted cast could be caused by swelling. I would advise you to be patient as recovery and swelling will take at least 9-12 months or more. Follow up with your surgeon as schedulled

You have a legitimate concern, and you should definitely check with your surgeon.  However, in many cases the appearance of the cast and / or tape immediately after surgery has very little correlation with how the nose looks underneath.  There can be uneven swelling on one side or the other, and if tip work was done, the tip of the nose is often taped with an exaggerated upturn.  Your surgeon is your partner in this process, and therefore will want to address any such concerns you may have.