Yes, if you were not given an arrival gift upon arrival, you can ask the hotel to pony up on the cash guarantee.

Just go down and let the front desk staff know. They may offer you the arrival gift at that time. If you really think they dropped the ball and should pay the guarantee and you have every right to do so, then stick to your guns and tell them that they didn't offer it upon your arrival. And as such, you are invoking the cash guarantee. They may still offer resistence and you may need to ask to speak to a manager. But per the rules, you should be offered the cash. (Sometimes they may instead offer some "extra" items or points, if those are acceptable, you can always accept those. But if you don't want those and prefer the cash, tell them no.)