On creating physical boxart and cartridge/cd labels

[SkyHighGam3r]

(If this doesn't sound HyperSpin related, it's because I haven't taken the time to explain, I'll show that off soon.)

I'm trying to print out some custom box-art... I created a new photoshop document with the right inches/mm sizes in Height and Width.

The problem is the image seems very blurry at this size... is there a way to increase resolution of an image like this? Keeping in mind that I will be printing this out on some gloss (semi-gloss?) paper...