Is it ok to cut the understrap off a life jacket or just not to wear it...I can't really swim but I don't think I need a strap between my legs. I thought that was only for kids jackets?

It is not good to cut the understrap off your life jacket. Even if you know how to swim. That strap, though uncomfortable, is there so the neck line of your lifejacket doesn't come up and into your face. I suggest you wear it.