Express/node.js debugging error: Error: Can't set headers after they are sent

I'm trying to create a basic CRUD application some trouble with debugging. To build my crud application, I'm currently using node.js, express, and mongodb. Any help that you all could provide would be really really helpful.

context: for reference I'm using this:

https://zellwk.com/blog/crud-express-mongodb/, currently on "Showing quotes to users" 

my problem: i'm getting the following error with my code and i'm not sure if this is due to the placement of my code.

Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:357:11)
    at ServerResponse.header (C:\Users\hcqph\gitprojects\crudbeta\node_modules\express\lib\response.js:725:10)
    at ServerResponse.contentType (C:\Users\hcqph\gitprojects\crudbeta\node_modules\express\lib\response.js:558:15)
    at ServerResponse.send (C:\Users\hcqph\gitprojects\crudbeta\node_modules\express\lib\response.js:145:14)
    at done (C:\Users\hcqph\gitprojects\crudbeta\node_modules\express\lib\response.js:962:10)
    at tryHandleCache (C:\Users\hcqph\gitprojects\crudbeta\node_modules\ejs\lib\ejs.js:208:10)
    at View.exports.renderFile [as engine] (C:\Users\hcqph\gitprojects\crudbeta\node_modules\ejs\lib\ejs.js:412:10)
    at View.render (C:\Users\hcqph\gitprojects\crudbeta\node_modules\express\lib\view.js:128:8)
    at tryRender (C:\Users\hcqph\gitprojects\crudbeta\node_modules\express\lib\application.js:640:10)
    at EventEmitter.render (C:\Users\hcqph\gitprojects\crudbeta\node_modules\express\lib\application.js:592:3)

this is my code:

app.use(bodyParser.urlencoded({extended: true}))

//set 'ejs' template engine, and default extension is ejs
app.set('view engine', 'ejs')

/* -------- for team documentation --------
=> = replacement for function

app.get hand a GET request (read operation)
------------------------------------------------ */
app.get('/', (req, res) => {
    //serves index.html back to browser
    res.sendFile(__dirname + '/index.html')

    //gets list of trips from mlab.com
    var cursor = db.collection('trips').find()

    //retrieves list of trips retrieved from mlab
    db.collection('trips').find().toArray(function(err, results) {
        if(err) return console.log(err)

        //renders index.ejs
        res.render('index.ejs', {trips:results})
    })
})



/* app.post handles a create request */
app.post('/trips', (req, res) => {
    db.collection('trips').save(req.body, (err, result) =>{
        if (err) return console.log(err)

        console.log('saved to database')
        res.redirect('/') //causes browser to reload
    })
})

is it because of where i'm playing my app.set? how can i fix this?

in addition, am i referencing my res.render for index.ejs properly if it's nested within folder views?

via Clark