Answer: Based on your description I am not able to tell you how to arrange the blocks. I would suggest you return to the store and ask for help in determining the best in way to form the circle at the diameter you need with the blocks you have.
I should mention that when planting around a tree it is best to leave the area right around the trunk unplanted so that you do not interfere with the trunk flare. Also, you would not want to raise the soil level at the trunk area because doing that interferes with air reaching the roots. Finally, heaping soil or mulch right up against the trunk can cause damage to the tree and also encourages diseases and insects. So, you may find that creating a border of flat pavers laid at or just below the soil surface is the best way to go, assuming you can place them without damaging any widespreading tree roots.
Good luck with your project!
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