rapidly growing mold on flat surface
Mold is a general name for many species of Fungi, which are heterotroph so they need organic material to feed on. You can see them grow on fiberglass because many organic material can accumulate near or on fiberglass (skin cells, plants root hairs, microbes, oils) and become substrate for the mold.
If you want to grow a specific mold you should first identify it to find the best substrate for that species and not for other. If you simply want mold you can use some kind of starch on the fiberglass and keep it moist (not wet, wetness will give you also oomycetes and bacteria). No need to spray it every 2hrs. You can close the fiberglass with a box, dark box is better (bacteria grow best with light).
You can take (with mask and gloves) some mold and put it on your fiberglass to promote the growing of that mold.
Describing your mold or posting a picture can help to identify. If you see two different colors report both of them and location (center, periphery)