QUOTE:
Hi! When I upload my photo, it looks pixelated on the product mockup.
It is a high quality 300DPI image, 4500x5400px. Does this happen to everyone?
Use the "Toggle Full Editor", it will look clearer.
The images are saved as 2200 x 3000 @ 200 DPI when exported to tshirtgang. Your images are larger than required, but no worry, they will be resized for printing when saved.