There are days I still don't feel like I have it together and December will be 3 years for me. If you really think about it, 6 months is not that long at all on an active cardiac floor. There's a very wide scope of information that you have to understand and figure out how it all weaves together which takes time. Instead of thinking how little you know, try to think about how much you have learned.
I can remember when I was a newly minted RN on my floor and the very thought of having someone in active chest pain scared the dickens out of me. Sure, I knew what to do, but I hadn't done it. Then late one night I had a patient decide to clot off the the 5th out of his 5 grafts. 10/10 crushing chest pain, he's freaking out, his wife is freaking out, I'm freaking out. I'm giving nitro, morphine, starting a nitro drip, more morphine, beta-blockers, the works and finally as the sun was coming up transferring him to the ICU. But I learned a lot that night. Now, when someone has chest pain, it all becomes near-automatic. I know what I'm doing - but importantly, I know why I'm doing it. That first night I'm going, "Beta-blockers? Why?...OK if you say so." Now I can ask the doc if they want it in an evolving case. You learn as you go.
Last summer we hired a big bunch of new nurses and I watched as they struggled through and between 6-8 months in they started to "get it" some faster than others, but nonetheless, still they were getting it. And those that felt the exact same way you do all asked the same thing as you. And I counter with the same thing: look at what you HAVE learned and achieved, then start looking at where you feel you're weak. Some positivity can go a long way y'know?
And for awhile, nursing will be task-oriented for new nurses, that's a given. Until you can get the tasks under near-robotic control, having the time to think about the bigger picture is rough. Be patient, it will come, just give it some time.