Featured Image thumbnail not resizing

I’m having an issue getting a featured image thumbnail to resize inside a post. The image doesnt automatically scale down to fit inside the my default thumbnail size of 150 150, resulting in an empty thumbnail box, as well as a full size image overlapping. I’m sure this is a pretty simpy fix, I’m just missing something. See the example below. Thanks

https://buymanthings.com/2013/06/18/woodmans-pal-military-premium-fixed-blade-knife/