Okay,youre not the first and wont be the last to burn a bit of pastic.A microwave is fine for DIY but you have to get used to the power/heat output so all microwaves are different but its really easy.
Start with about 200ml in a pirex jug.Blast for a minute and half.Give it a good stir and then blast for a minute or so.Get a feel of how long it takes to turn the plastic to clear.After it turns clear I use 20 seconds blasts.Do this until you have the right consistency.After every pour wipe the spout clear with some kitchen paper,this helps alot.Also when you stir the plastisol you will have some on the sides of the jug,before every pour take a knife,run it round the jug and remove this.Keep this aside,after I've finished pouring that colour I normaly throw this back in the jug for another day,recycle,recycle.
Remember add your colour and glitter near the end.First to burn will be the centre of jug at the bottom so when stirring tilt the jug to the side.