Question: How make it error be small in iteration and how act with imaginary part?

in my iteration when i got answer the error is so big and the method is powerfull i don't know i did mistake or my exact function i have to change it, becuase error is so big , how i can make error be smaller i did any mistake ?
and how i can plot them together exact and approximate in one graph also 3D and 2D

Num-e1.mw

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