I'm not familiar with the full instructions for Dylon but aren't dilution, times, temperatures and rinses critical. You'll have no control over those in a washing machine.
I've never had a good result home-dying whatever method I use.
It's hard to get good coverage when done by hand, especially large items like curtains. If you do it in the machine the dye lingers and stains everything you wash afterwards.
Buy the dylon for machine wash dying. I have used many times very easy and no problems with colour staining future washes after following all instructions
If it's hand dye you haven't got enough.... Even a pair of smallish curtains needs two boxes of machine dye. It also depends on the fabric only pure cotton or linen dye true. Always use a bit more than they say.