Why doesn't the back look as good as the front?
One of my biggest problems when I was learning how to handsew is that, while the front looked more or less ok, the back was a mess. It took me a while to figure out how to fix this.
One reason this happens, is that your needle is going in at a diagonal and not straight up. If you are doing your running stitch one stitch at a time (needle down, pull, needle up, pull) it helps if you check the back every time you make a stitch at first, to train your hand to put them in the right place. Another way to fix this is (if your fabric is thin enough to allow it) is to make one whole stitch in one go (down up, pull). With this, you really need to watch not only the length of the stitch, but the length of the negative space between the stitches, as this is your stitch on the back.
Now, if it's just a matter of some stitches being longer than others, you can always cover it up with a flat-fell seam. Uneven stitches running diagonally to the seam can affect the way the garment sits and falls, though. I know it's frustrating, but don't hesitate to take out part of a seam and re-do it! You'll be happier in the long run.