Flutter cannot add the button, always error

Question

I want to add a button above the box, I will put the code here. I've tried to add another container, child, and children, but it is always an error, can someone help me with how to make the button? I want to add it after the end of this code, Thanks

body: 
        Container(
            padding: EdgeInsets.all(20),
            child: 
            Column(
              children: [
                SizedBox(height: 20,),
                Text("Welcome", 
                style: TextStyle(fontSize: 20, fontWeight: FontWeight.bold, color: Color(0xFF7C99AC)),
                ),
                SizedBox(height: 15,),
                Text("${data['name']}", 
                style: TextStyle(fontSize: 30, fontWeight: FontWeight.bold, color: Color(0xFF7C99AC)),
                ),
                SizedBox(height: 10,),
                Padding(padding: EdgeInsets.only(top:20),
                child: 
                Container(  
                  height:300,
                  child: GridView.count(
                    crossAxisCount: 2, 
                    crossAxisSpacing: 12, 
                    mainAxisSpacing: 8,
                    childAspectRatio: 1.30,
                    children: [
                      _parkingslot(name:'Floor'),
                      _parkingslot(name: 'Slot Number'),
                      _parkingslot(name: 'Check In Time'),
                      _parkingslot(name: 'Parking Fee'),
                    ],
                    ),
                    
                  ),
                ),
              ],
            ),              
        ),