I'm an amateur in the world of photography, and I'm coming upon an issue I can't seem to solve.

I'm trying to take portraits and such where the object is in focus, and the background is very blurred.
In the preview it looks good, however when I actually take the photo and look back on it, the background is not as blurred as it was in the preview.

I've tried messing with the settings and changing lenses and stuff but it doesn't seem to work.

For example, the preview looks like this:


I'm using a Canon Rebel T5.