Hi! What you need to do is to go back the mushroom area and do everything you did prior, but stop when you get to the Red Mushroom that has 2 smaller ones on each side of it. (Seen right here)
Then after you go up to the Red Mushroom and have both mini-shrooms disappear, you want to go to the right where it has a jumping patch.
(Seen here)
Step onto the patch and let it bring you back to start. After that, you want to head back to the Patch Jumping area and if the Faded Mushroom is now red, you'll be able to get the 4th Gracidea! (Seen here. I hope this helps! These Red Mushrooms will indicate that the mini purple mushroom blockade are gone.)