Hi guys, as the question says, how do I not appear soft?

I've got this new job and basically they've said I'm a good fit for the company. I'm friendly and positive and get along with people well, but their only concern is that I'm a bit soft.

I see where they are coming from, but I'm not sure how to change it. I believe it is just an aura that I give out some how. Normally it's something I'd just change, but I'm not sure what traits I'd need to change to address this.

(Note: It's not a physical thing. I'm 6'1, hit the gym and am regularly told I look like a Viking or that Im in a motor bike gang.)