I'll go out on a limb here and say that the actual SOUND of the vocal is pretty decent, especially considering the equipment used. But you're singing totally from your throat and nose - it makes for a really weak sounding vocal... Some people pull that off brilliantly (Tom Petty, Michael Stipe), but you HAVE to be dead on pitchwise in order to pull it off, and you're just not on this tune.
I'm no vocal coach, and honestly, I've seen a lot of them do more harm than good, but you have to find a way to sing that works for you... Let me ask this; can you HEAR that it's off pitchwise? If yes, then you can fix it by doing maybe more than one or 2 takes. The tentative way you're singing reminds me of the way most people sing when they're not used to singing with headphones on -- if that's the case, take one of the cans off of your ear when you're singing...it's amazing how much more confidently you sing when you can hear some of the room.
Also, try doing a lot of takes. I usually do a ridiculous amount of vocal takes, then I splice the best parts of each together. Tedious as hell, but in a tune like this, the vocal is definitely front and center, and you wanna' spend more time on that one element than probably anything else.
I know this is a mixing clinic, but the best mixes are born from the best tracks possible, and the biggest problem with this mix, in my opinion, is the vocal. There are other things...like some lags in tune where there's really nothing going on that you might want to fill with a little guitar lead or ...hell, whistle or something, lol...but the main problem, I think...is the vocal.
Just my opinion. Good luck.
Chris