Tracking steps that are not there.

I have an apple watch, I really wanted something to help with my fitness goals and I thought this would be great for that. I work at a retail store where I have to drive a forklift. The forklift speeds reach 15mph sometimes but I find even though I am driving all day the stats on my watch are adding up. So when it says I walked 3.51 miles I am a little skeptical is there a ways around this please help.