Whenever I've run into that I typically strip off the recently applied dye paint using lacquer thinner and then start over. Before you apply anything new, test it on the back side and let it set up for a day.
When using lacquer thinner, you should wear some decent chemical gloves and work outside in fresh air. A good chemical mask can also be helpful. Be careful of over scrubbing the plastic since the lacquer thinner will soften the material. Using lacquer thinner on vinyl plastic like this is called 'burning' and it will do a pretty good job of prepping a piece before painting. I use plenty of rags (usually old towels work best) and change them out frequently after they become saturated with the old paint/dye. Spread the old rags out on the ground and let them dry out completely before disposing. Depending where you live, you may have to find a chemical disposal to take them in the end. This is kind of an 'old school' approach, but I'm not sure if there is anything else on the market that will effectively remove it without damaging the vinyl. Because the current dye is fresh, it should come off pretty fast.
You can apply new dye paint over the previous coats, but you will quickly begin to lose the pebble grain finish. I'm sure others will chime in with alternative methods.
