Blurry banner Image

My banner is blurry.... Yet the image I uploaded for it was perfectly sharp, no noise, and fit the stated requirements (at least 400 x1400pxls, jpg format, AdobeRGB embedded, and under 2 Mb). Making the image larger or smaller before uploading doesn't do anything. It's not a good look for my storefront. Can anyone tell me why this is happening or how to fix it???