12 year old watching newborn for 15 minutes?

Okay so I need to run to the store real quick which would take 15 minutes it’s like 2 blocks away. I trust my 12 year old she’s very mature for her age. I have my 3 week old baby that I’m hoping to put to sleep so I can run real quick but idk if I’m being irresponsible by letting my 12 year old watch him? Any advice?