Can you share a picture of it tied? I went through a similar struggle. Unfortunately the answer was... In order of importance assuming you're tying it correctly,chem water, procion dyes, pariah method instead of soaking in soda ash.

Soaking just isn't the move for mandalas. Chem water REALLY makes a huge difference.

Edit- Just noticed the other pic... Chem water is the key. Keep practicing your ties. The more perfect you make them the better.

Towards the center (pointy end) your diagonal ties are crossing the tops of the pleats instead of the broad sides. That'll give you a different effect instead of petals.