gas stove on for hours risk to dog?

I just moved into an apartment and as I was cleaning the kitchen I noticed a gas smell. I had not even touched the stove yet so I assumed there was a leak.. turns out the landlord walks up and says the burner was on all day. My small dog was in the apartments (387 sq ft) with just one window open... what risks does this pose to my dog? I was out most of the day running around buying things for the apartment so I was not home much but I am so freaking worried for her right now