Is my carrier just too small?

I am flying with my dog for the first time. He is an 19 lbs chihuahua beagle mix. The airline dog carrier requirements are 17" L x 8" W x 13". My dog can turn around and lay down but it is a soft carrier so he is pushing against the sides to do so. He has JUST enough room to lay down, no extra space at all. I think he gets scared in tight spaces as he seemed a little uneasy. I have never had a dog previously or flown with a dog so I am just not sure if this is too small.