I'm pretty sure this is the greatest shirt I've ever seen...I must have it. Raid17, if you read this...is there any way I can get this shirt?

I've created a design and submitted it for critique and later found out that it needed to have a resolution of 150dpi. I came to find out that I had been working in 72dpi. I know how to change the resolution, but when I do my design becomes blurry. I was wondering if any of you could possibly tell me how to prevent this from happening or fix it in any other way that wouldn't require me to completely re-draw the design. I'm working with Photoshop.

Thanks a lot!