nodejs is database created double using res.render?

I write some nodejs code to make a to do list, using express, ejs and mongoose when i write this code:

const itemShema = new mongoose.Schema({
        name: String
    })
    const Item = mongoose.model('Item', itemShema);
    const item1 = new Item({
        name: 'drink water'
    })
    const defaults = item1;
    
    const listShema = mongoose.Schema({
        name: String,
        Items: [itemShema]
    });
    const List = mongoose.model('List', listShema);
    
app.get('/:custom', function(req,res){
        let routes = req.params.custom;
        List.findOne({name:routes}, function(err, showItem){
            if (err) console.log(err);
            else{
            if (!showItem){
                const listName = new List({
                    name: routes,
                    Items: defaults
                });
                listName.save();
                console.log(routes);
                res.redirect("/" + routes);
            }
            else {
                res.render('list', {titleList: routes, items: showItem.Items});
            }
            
        }
        });
        
    });

Basically i want to create a dynamic url and get value of what i triggle by using req.params.custom. Then i create new list (example: /home) and check if that list exist data by findOne({name:routes}. If not exist -> create default data and redirect, else -> res.render ejs file that i set tiltle is routes and items is showItem.Items

=> The problem is when i run this code, it create 2 same databases name:'home', Items: ['drink water'].

I have no clue that why it create 2 and how to fix it, i just want to add 1 default data Please help me!