Then you have two problems..
Rit dyes are NOT good for tie-dye, they are more for dyeing all one color..
The color isn't very bright on them, any its just not a good dye to use for it IMO..
Its better to goto a craft store (or maybe even wal-mart?) and by a tie-dye kit.. or the dyes they use in the kits.. A good kit is Rainbow Rock.. they have a couple.. bright/pastal/whatever just pick a good one for you.
Mainly your looking for Fiber Reactive Procion Dyes the craft store "michaels"
has the kits and the dyes you can buy.
Then folow the directions.. should be something like...
mix presoak together and let shirt in there like 10 minutes.
wring out shirt..
while still damp twist and tie it however you want.
apply dies
wrap wet/dyed shirt in platic (to keep it from drying out) and let sit 12-24 hours.
unwrap and rinse out whole shirt untill water runs clear.
wash and enjoy!