Problem with Contours at TH2F

I have the problem with contours.
I have a datasheet with 6 variables: x,y,z,Bx,By,Bz
Now I want to plot a x-y Square and Bz as the contour at a special Z-Pos.
But i dont know how to set Bz as contour…

Here my Code:

#include "Riostream.h"
#include "TTree.h"
#include <fstream>
#include "TH3.h"
#include "TH2.h"
#include "TH1.h"
#include "TGraph2D.h"
#include "TStyle.h"


TH2F *Contour (const char * filename){
    
        Float_t x;
	Float_t y;
	Float_t z;
	Float_t Bx;
	Float_t By;
	Float_t Bz;
	Float_t zpos;
	Float_t ypos;
	Float_t xpos;
	
    TFile *file = new TFile(filename);
    TTree *tree = (TTree*)file->Get("Daten"); 
    tree->SetBranchAddress("x",&x);
    tree->SetBranchAddress("y",&y);
    tree->SetBranchAddress("z",&z);
    tree->SetBranchAddress("Bx",&Bx);
    tree->SetBranchAddress("By",&By);
    tree->SetBranchAddress("Bz",&Bz);
    
    Int_t nentries = tree->GetEntries();
    
    tree->Print();
    
    cout << endl << "Z-Position: "; 
    cin >> zpos;
    
    TCanvas *c1 = new TCanvas("c1","Canvas", 0,0,700,600);
    TH2F * xyBz = new TH2F("xyBz","Bz over xy",100,-30.,35.,100,-30.,35.);

    

    for(int i=0; i < nentries; i++){
        tree->GetEntry(i);
        
        //Read Data for special Z-Pos and add in Hist
        if(z>= (zpos-1) && z<= (zpos+1)){
            cout << x << "  " << y << "  " << z << "  " << Bz << endl;
            xyBz->Fill(x,y,Bz);
            
        }
    }
    gStyle->SetPalette(1);
    xyBz->Draw("CONT4Z");
    xyBz->SetMinimum(0.03);
    xyBz->SetMaximum(0.04);  
    
  
    
    
    return 0;
}

The graph looks like that:

But I want it more like that, how I plotted the same Data for Z = 200 with ORIGIN

Hopefully you can help me.
data.root (9.75 KB)



Bz_over_xy.pdf (190 KB)

I think there is some pictures missing in your explanation …

Its actually not missing, but it doest appear. As a picture
Its the attachment under the picture you see.
Bx_over_xy.pdf

Oh yes sorry …

your binning is not good. draw it as a lego and you will understand that there is no way to draw contour around these peaks…

Okay thank you.
I reduced the number of bins.
Now it works, how I want.
This was only a test datasheet, so there will be more points and the contour should work.