The first time you heat virgin plastisol it needs to get to about 350*. Any reheats after that 300-325* should be good. Dont want reheats too hot or plastic will scorch, change color, and glitter will melt.
I would use a couple ounces of virgin plastic and then add a "squirt" of heat stabilizer and then some used plastic for remelts. If it bubbles or foams that means there is moisture in there. Water and plastisol is a bad mix. Stir stir stir.
Keep batches small till you learn so you dont waste plastic. Go at least 4 oz and no more than 8 oz.
GL and stay safe. ALWAYS wear gloves