Why won't my bacteria grow? I used 'Bacto-Agar'. Does that have anything to do with it???

I have a science fair coming up in like a week, and I'm supposed to be growing bacteria, and I already did my experiment and I already swabbed the Petri dishes and everything, and I put the Petri dishes in a warm spot, but nothing has grown, and it's been a week. i used bacto agar, so am i supposed to put like nutrient broth in or something??