Good luck with it bro, it is very tricky and frustrating but don't let that discourage you. I suggest you write down exactly what you used and the measurements and when it crashes write down how long it took and work from there with your ratios. I will tell you it will crash and it does suck because you lose the money you spent to buy all the materials but chalk it up as a learning and try again. It may take till it cools to crash or maybe the next day or like I said before two weeks but give it time and watch it and you will notice when it is starting to crash, just wait it out and eventually you will get it to hold completely, I say if it don't crash in a month it is good and wont crash after that either. It took me 100 grams of powder and months of waiting and watching it, so be patient.
Thanks
TMM