Driving today, 45 mph, car dies. Restart it, does it again after a mile or so. on 2002 Volkswagen Cabrio

Could it be the fuel line? Very random, last time put regular fuel in, about 1/2 tank left, put premium in this time. Bad idea? Mixing that is - should I have waited til the tank was a bit lower then added the premium gas?

Asked by for the 2002 Volkswagen Cabrio