Lorraine - from Perth, Western Australia
After drying out for a week, your fondant decorations should have been completely dried out and hard. After you attached the fondant decorations to the cupcakes, did you put them in the refrigerator? Extra moisture from the refrigerator may have caused the decorations to sag. They are better left at room temperature.
Next time, try making your decorations with a 50/50 blend of fondant and gum paste. Gum paste dries out much more quickly than rolled fondant, and it never wilts under moisture. By using a blend, you get the ease of working with fondant along with the strength and structure of gum paste. You can buy ready-to-use gum paste at major craft stores.