NM Need Quick Answer for DIY STD From Vistaprint

I made a STD for my sister and uploaded my own design. When I click on the print preview..it's coming up blurry..like a low resolution file. I noticed that with their templates, it also comes up a bit fuzzy. Do they print them in high res so they come out clear?

ETA: I called Vista and they emailed me a proof for free and it was perfect!