How to increase object time length on Adobe After Effects?

I'm really struggling to make an image continue/loop in the timeline for more than 6 seconds. That was the maximum it allowed me to extend. It was originally 2 milliseconds long. Furthermore, there are some bits on the image that are supposed to be "see-through" with a transparent background but for some reason, when I apply the "fill" effect, it covers those bits up. Only to let them "see-through" again out of nowhere in the timeline, without me adding any other effect or animation to it. Could anyone please help me understand what I'm doing wrong and why this is happening?