[Cyber Warrior]

Ok so lately I have been learning my way as a graphic designer, not to make a career out of it, but to use it whenever I need to make some graphic for personal use. So I have a youtube channel, and decided to change my cover photo. I opened my Adobe Illustrator and used 2560x1440 dimensions for cover photo. After little work I exported that image as .png and uploaded on my youtube channel. But there was a problem, my photo was blurry, where was the problem? Designers I need some advice