BIG error

I can't believe what I did yesterday. I decide to make the hat for Gail. I knew it would take me a few hours. I had the yarn. I'm using the purple yarn left over from the fairy blanket. It's good yarn 100% marino wool, very soft. I did a test gauge, as always, and it worked out fine using 3 balls together. I also was able to use the plastic 3 ball separator that I got for free from Simply Knitting magazine, which worked great and stopped the 3 balls from twisting together. I casted on and counted. Or thought I counted. Now mine you I always count twice. And then knitted away. Knitting, knitting, knitting. Got to the part where the crown decrease started and it didn't work out. So I went to look for my mistake. I couldn't find it. I thought I missed k2tog or put k1 were it shouldn't be. I couldn't figure it out. So finally I decided to count my stitches. I was supposed to cast on 47 stitches and I had 42. OH NO!!! You see I count in 5's . 5, 10, 15, 20 see. I took the hat off the needles to see if it would fit anyways, NOT. It had to be Totaled, Frogged, Ripped, Gone! Start all over again. I wasted the day. Richard tried to ask isn't there any you can do to it so you wouldn't have to rip it. Isn't there anyone with a smaller head. I couldn't think of anyone. NO NO NO. So I ripped it and rewound the yarn into 1 big ball. Casted back on and counted 3 times. and after a few rows counted again. I sure I am not the first one that this has happen to. And I'm sure that this is not the first time that this has happened to me. Blocked it out. Time to get back to knitting.