If you plan to unmold your panna cotta for presentation, be sure to chill it for about four hours before you try to release it. And if you run into any trouble, there are a few tricks to try if you encounter some stubbornness from your delicate dessert.
The perfect panna cotta molds are small, only about 5 or 6 ounces (to hold about 4 ounces, or a half a cup, of your mixture). You'll always turn out perfectly-shaped panna cotta if you give yourself a little insurance before filling those molds. Oil each mold with a neutral, flavorless oil -- and use a light hand while doing so -- for best results.
And if your panna cotta just won't release, what's the harm in eating it out of its mold? Avoid this whole problem by pouring and setting your dessert into containers intended for serving.