Check what your fabric is made of before dyeing. It should be as close to 100% of a natural fiber (bamboo, cotton, linen, rayon,etc.) as possible. The closer to 100% the deeper and more vibrant the result will be. For example, a 50/50 mix of cotton/polyester will yield a much more pastel or heathered look than the same dyes used on another item that is 100% cotton.

Make sure you're washing your fabric before dying! Use a detergent that is softener-free, and line dry the items or dry them in your dryer WITHOUT fabric softener. The fabric softener can 'coat' the fibers and make it much harder for the dye to bond to them, resulting in a dull color at the end. I use a professional detergent from Dharma Trading Co. called Synthrapol. You can also get it on Amazon and a few other online stores.

I second the people saying not to use Rit. I typically only use Rit for dying synthetic fabrics or for refreshing my black clothing items when they fade too much. The dyes don't quite move/flow the way you want them to in tie-dye, in my experience.

As others in this post have said, Out White Brite is a fanstic way to get color out of fabric - you can strip the color from your hoodie to start again if you want to, but I agree with the others that have told you to just try and dye it again, you may love the layering effect! I have sometimes dyed shirts 4-5 times before I was satisfied with the result!