Make sure you’re using Merge Cube in a well-lit area. If you need more light, the app has a feature that will turn on your smartphone’s flashlight. Tap the menu icon, then tap the flashlight icon.
If you lose the holographic layer and see the physical cube, you might be holding your Merge Cube too close or moving it too fast. Your hand might also be blocking the cube’s graphics. Try moving the cube around, having a flat cube side facing the camera and repositioning your hand.