I am sure there are others out there that have more experience that could help you better, but here goes for a start, maybe you can find some tid bit of info here that may help you.
First you need to get some sort of vacuum chamber and pump set up. Best Value Vacs have an economical, universal vacuum lid that will fit different sizes of standard cooking pots you may have at home. You will also need a vac pump. There are many economical options for a vac chamber and pump. An additional and useful option is to get a temp gun as well. You already have a hot plate but the addition of a heating pad to wrap the top/sides of the vac chamber to keep a more uniform temp will also help. Keep checking the temps, you are basically trying to dehydrate the oil not cook it, so keep the temps down. I suspect of your problems may have been too high of heat in your heat purge. Heat purge works for good oil but not as well for shatter.
Start off your vacuum purging with a temp at about 90 and start flipping your slabs over as soon they are stable enough, remember the temp at the bottom of your slab is different than the temp at the top of your oil, so periodically flip em and re-vac. Gradually increase your temp up to around 98 and finally to around 108 maximum (as the slab hardens it becomes increasingly difficult to extract the remaining butane and the temps must slowly rise). Using too high of heat is your enemy to making good shatter. The heat at the surface of your hotplate will be different than at the bottom of your slab and different from the top of the slab. Spread your BHO as thinly as possible when you start, you can always fold it over and in on itself as you go. Take some time and experiment with your time schedule for purging. When you think its done let it sit out overnight and see what the consistency is like once the slab cools down to room temp for awhile, and re purge as is necessary.
Keep tasting and testing and trying, you will get there. Keep an open mind to all things possible, everyone has their own ideas and with a little discrimination you should come up with a system that works for you.
A Dab a Day will keep the Doctor at Bay!