Since Lowcoder v2.6 we have now introduced a better preview.
The main idea is this: As your app with the settings "Autofill" will use the full window-size, you should imagine the whole canvas as your app. Currently it looks like you placed the app contents in the form factor of a mobile app in the middle of the canvas.
By the responsive feature, now Lowcoder treats the whole canvas as the window width of the mobile browser - and this naturally squeezes the view.

In the App preview we built the ability to choose mobile and tablet as possible form factors - so you can see this earlier and play with the effects.

Have also a look to the responsive layout component. We optimized it, so more use cases for mobile / tablet view can be realized.