You should wait to use the fabric until you feel good about the amount of color coming out. If you are not using white, you might be ok. Responding on another thread today about the only problem I've ever had was with maroon bleeding onto my white and turning it baby pink.
I think Retayne is the product you are looking for. There is also Rit Color Stay. Soda ash is more used to prepare fabric for dying than using it as a fixative but might be worth a shot. The Rit and Soda Ash can often be found with tie dye kits at Walmart!
There are other things you can do like heat treat, depending on how much fabric you have...
Don't use in your washing machine but with troublesome fabrics I like to do a bit of a soak with a small amount of original Dawn dish soap.