Firstly i am going to say don’t get to stressed by your knitting, remember it is supposed to be and enjoyable hobby. Secondly i couldnt agree more, sometimes knitting rage does happen. There is a very tangled skein of yarn that has been living under our sofa for several months now and won’t be allowed out until it as thought about what it has done. It got flung there.
now for the un-knitting. The quickest technique, especially if you have a lot of stitches (several rows) to undo is frogging, or ripping somthing out. that means you take you take out your needles and literally unravel the knitting. You don’t have to go all the wayy back to the start, you can stop at a correct row and reinsert the needle into the loops. Ifind that a bit tricky somtimes so a very usefull method is to reinsert a needle into the ‘destination’ row before you start ripping and the yarn will stop there with the loops magically on the needles the right way!
The other method, which is my prefered method, is tinking or un-kniting stitches. This is ideal when it is only a few stitches, although i have been known to go back several rows doing this due to my hate of frogging. To do this you insert the tip of your left needle into the loop under the stitch on your right needle. slide the stitch of the right needle and give a little tug on the working yarn to free it, you now have an unworked stitch on your left needle.
there is a much better description and some nice clear pictures of both techniques on this page from Knitty.
This site also has a video on picking up stitches after frogging and how to insert a needle before frogging. just scroll down the page to the 'fixing mistakes section.