I made this today and took the comments into consideration by using more water (about 280g) and it was completely un usable. I had to make 2 batches as I wanted a few different colours (mixed in the colour after) and by the time I completed the second batch the first batch was literally like solid jelly. I chucked the whole lot and started again using the same instructions just with my own quantities
I used 600g of water, 25g of cornflour and about a teaspoon of vegetable liquid food dye in each jar and this is the result I got.