OpenGL Fullscreen

I modified an OpenGL program I made so I could toggle fullscreen.

It seems to go into fullscreen just fine, but when I try to toggle back, it remains fullscreen and it just shows the titlebar. How can I get it to convert back?

Code:

HWND CreateMyWindow(LPSTR strWindowName, int width, int height, HINSTANCE hInstance, bool fullscreen)
{
  
    HWND     hWnd;
    WNDCLASS wc;

    DWORD dwExStyle;
    DWORD dwStyle;

    RECT rWindow;

    memset(&wc, 0, sizeof(WNDCLASS));
    wc.style         = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;
    wc.lpfnWndProc   = WinProc;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(NULL, IDI_WINLOGO);
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_3DSHADOW + 1);
    wc.lpszClassName = "Chip8";

    RegisterClass(&wc);

    g_hInstance = hInstance;

    rWindow.left   = 0;
    rWindow.right  = width;
    rWindow.top    = 0;
    rWindow.bottom = height+15;
    
    if(fullscreen) {
        
        DEVMODE dmScreenSettings;
        memset(&dmScreenSettings, 0, sizeof(dmScreenSettings));
        
        dmScreenSettings.dmSize         = sizeof(dmScreenSettings);		
	dmScreenSettings.dmPelsWidth	= width;				
	dmScreenSettings.dmPelsHeight	= height;			  
	dmScreenSettings.dmBitsPerPel	= 16;
	dmScreenSettings.dmFields       = DM_BITSPERPEL | DM_PELSWIDTH | DM_PELSHEIGHT;
		
	ChangeDisplaySettings(&dmScreenSettings, CDS_FULLSCREEN);
  	
    }		
    
    if(fullscreen) {
        
        dwExStyle = WS_EX_APPWINDOW;
        dwStyle   = WS_POPUP;
        ShowCursor(FALSE);
        
    }        
    
    else {
    
        dwExStyle = WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;
        dwStyle = WS_OVERLAPPED | WS_MINIMIZEBOX | WS_SYSMENU;
        
    }    

    AdjustWindowRectEx(&rWindow, dwStyle, FALSE, dwExStyle);

    hWnd = CreateWindowEx(dwExStyle, "Chip8", strWindowName, WS_CLIPSIBLINGS | WS_CLIPCHILDREN | dwStyle,
                          0, 0, rWindow.right - rWindow.left, rWindow.bottom - rWindow.top, NULL, NULL, hInstance, NULL);

    if(!hWnd) return NULL;

    ShowWindow(hWnd, SW_SHOWNORMAL);
    UpdateWindow(hWnd);

    SetFocus(hWnd);

    return hWnd;
    
}

When you switch back to a window you'll need to restore the desktop settings with

Code:

ChangeDisplaySettings(0,0);

See description for lpDevMode in ChangeDisplaySettings.

Thank you.