Installing one way light switch
You have two problems here:  one, hacking a two way switch where you ought to have a three way switch, and two, using a ground as a current carrying conductor.  You should put back the original three way switch immediately to be safe, and come up with a plan B.  

Resolving the first problem is simple:  buy a smart switch made to replace a three way switch.  

Resolving the ground wire issue is a little more difficult.  Your smart switch requires a neutral, but the box it's going in doesn't have a neutral.  (At least not that I can see in the photo.)  This is common when switches were wired with a switch loop, which is what it looks like you have here.  

You have used a ground wire in place of a neutral.  Using a ground wire in place of the neutral works, but it isn't safe.  The ground wire should only conduct current in the event of a ground fault.  So you shouldn't have bootlegged the neutral, it's a code violation and a safety issue.  

To rectify this, you could bring a neutral to the box by rewiring, that may be a small job, may be a big job, but it will work with just about any smart switch.  

You could also choose a different smart switch.  There are smart switches that work without a neutral.  Most of these actually bootleg the neutral internally.  This seems like a terrible idea, but UL will only list a switch that bootlegs the neutral if it is tested and only passes a very small amount of current on the neutral - small enough that it isn't a safety issue.  So if a UL listed switch does it, it doesn't count as bootlegging.  

Just make sure the switch is UL listed, and stick to a reputable brand - there are tons of products on the market from sketchy brands that are putting the UL logo on products that are not really UL listed.