My submission was rejected. I don't know if it was the Image or music.

I had an initial rejection but without specific reasons. I had a high quality image for my thumbnail that appeared to be blurry when scaled down to the 80x80 requirement. I may have not converted the file correctly. The original file was 2.6MP JPG 4032x3024. It was RGB color space and I think I saw somewhere they are looking for sRGB. I am new to this and not that savvy with file conversions and formatting etc. How can I convert the image to acceptable and how can I determine if my sound file was the issue? I would appreciate any help.!