I think it's time to introduce you to a new idea. Why not treat your three controls as a single control?
There is a type of class you can add to your project called a UserControl
] - it's a container that you fill with your controls, and add your code to make them work together. Then, when you want to add all of the controls, you create an instance of your user control instead, and add that - it handles adding the three controls you want to draw.
I would create one, add your textbox, combobox and button at design time, and provide an event which the parent handles to remove it when requested. That way, the remove code just needs to access your Panel.Controls list, and use the Remove method with the
parameter to take all three out at once...
(And it's really easy to do - but it makes your code a lot, lot simpler!)