Uneven horizontal and vertical gap for same value in wxWidgets

Question

In wxWidgets i have initialized a Grid Sizer called numpad. and I have my wxButtons array named as numbers. I just want my GridSizer to have even spaces, and as you can see in the image that I have set SetHGap(10) and SetVGap(10), still the spaces in G.U.I. seem uneven.

    wxBoxSizer* vertiSizer = new wxBoxSizer(wxVERTICAL);
    wxBoxSizer* horiSizer = new wxBoxSizer(wxHORIZONTAL);
    calcArea = new wxTextCtrl(this, CALCAREA, "", wxPoint(0,0), wxSize(100,60));
    calcArea->SetFont(wxFont(21, wxFONTFAMILY_MODERN, wxFONTSTYLE_NORMAL, wxFONTWEIGHT_BOLD));
    
    numbers = new wxButton*[10];
    wxGridSizer* numpad = new wxGridSizer(3, 3, wxSize(0,0));    
    for(int i = 0; i < 3; i++){
        
        for(int j = 0; j < 3; j++){
            numbers[i*3+j] = new wxButton(this, wxID_ANY, std::to_string(i*3+j+1), wxPoint(0,0), wxSize(70, 80));
            numbers[i*3+j]->SetFont(wxFont(20, wxFONTFAMILY_MODERN, wxFONTSTYLE_NORMAL, wxFONTWEIGHT_BOLD));
            
            numpad->Add(numbers[i*3+j], 0, wxFIXED | wxALL, 0);
            
            
        }
        
    }
    numpad->SetHGap(10);
    numpad->SetVGap(10);
    
    
    
    vertiSizer->Add(calcArea, 0, wxEXPAND | wxALL, 4);

    vertiSizer->Add(numpad, 0,  wxSHAPED| wxLEFT, 10);
    
    
    this->SetSizer(vertiSizer, true);