Help! Poor Quality Render

I am having a very poor quality resolution and bluriness in my final rendor (attached). I have tried increasing total canvas size and increasing the pixels per inch to 3000, but there is no change to the final product. Also, the background image that I imported appears to have gone down in quality as well. The image looks great by itself and is about 5000x4000 pixels, but when I import it to Dimension, the quality is greatly reduced.