First of all littlemoma107 Welcome to the forum!!
You did play a whole end in the game before posting here for help. Surely read a lot, didn't you?
Mushroom key? Have you got the key from Patooters, the stinker standing at the Market Place? When you played all the levels at the Mushroom Area, this could be your last key to find.
At the Ruins, you can play more than 2 levels to obtain a rainbow key. There are 4

or more levels at the Ruins. Not all giving you a rainbow key. But you can collect there 3 rainbow keys. That's for sure.
I don't know anymore in which level you get a key.
Your last token is in that free star area.
on the right bottom corner
On some occasions, like getting the letter to Noosee, you can get stars too by completing tasks in the game and not only by playing levels.
After the purple shard you can get an extra golden star from the Merchant (losing coins, that is)