It takes months to years of habitual overeating to physically stretch it out to any extent. It always stretches out a bit over time, but regardless of actual stretching, you will naturally be able to eat more as your stretch receptors in your stomach accept a bit more food over time.
Also, the stretching concern is only a concern if you are making bad food choices. Eating highly nutritious, non-processed foods low in sugar and sodium will keep you on track regardless of stretching. It all comes down to what you fill that space with, not so much about how much.