Dimension is making my renders pixelated.

Hello,

So I am trying to create some 3D mockups. But when I render, my background image is clear but my 3D objects render very pixelated. I have tried messing with the positions and camera, but nothing is working. I am using Ai files for the decals as well, and I noticed that the actual 3D model is pixelated, not just the images.

Here are some screenshots: