Wow, I'm surprised you haven't gotten more replies by now. Makes me feel like maybe it's just you & me! Because, yeah, I'm right there with you! Well, not all the time, but it's been a year and a half for me too, and I also feel nervous and edgy on my way to work, I think about work all the time at home, after coming home from work I have a hard time sleeping because I'm always running through various scenarios in my mind, what would I do if....xyz happened....what would I do first, then next, etc etc etc. I work in an ER so mostly traumas and CPRs are what I think about, MIs and strokes, anaphylaxis, stuff like that. I find that when I make a mistake, or even when I almost make a mistake then catch it, I agonize over it for weeks, thinking about how I should have known better.
But the good news is that it's getting better all the time, I'm getting more comfortable as I become more knowledgeable. And I read read read. I have just gotten my ER textbook out again and am reading it cover to cover. I read here on allnurses, I read nursing magazines, I have a Critical Care handbook that's really good. So I figure that at some point I will have seen and dealt with just about every major medical emergency or trauma that I can, and will be more and more comfortable as I gain that experience. One thing I did decide though, recently, is that because I've been having trouble sleeping, that I need to stop reading textbooks and nursing educational stuff at bedtime. I think it makes me think about it too much so that I can't get to sleep. I am going to start reserving my educational reading for day/early evening, but not right before bed.
Since I'm not in oncology I don't know about ratios.
I have made a conscious effort lately to change my attitude at work. I am usually very hard on myself, trying to get everything done right away. I see myself racing up & down hallways, for example. So last shift I decided "I can only do what I can do", if you get my meaning. I mean, no one can do everything at once, you can only do one thing at a time, and a nice brisk pace is fast enough, I don't have to race around all shift.
Anyway, my point is you are not the only one who still feels the anxiety even after all this time, but I really feel that it's a combination of continuous education and attitude that will help.