I assume your test-print is small? Likely not enough time to build up the amount of charge (or whatever) required to mess up your print.
You can kill static with humidity, there are also a few hacks that involve dryer sheets and Christmas tinsel. However, before you go chasing that white rabbit, clean the thing, make sure your head-height isn't set to "high" while you're printing on vinyl (not sure how the VP 300 deals with head-height, but w/e) and make sure that your machine is on a level surface, the basics.