when I first started knitting I was paranoided about dropping stitches. as a result I would "in round through in round through off" or see the bar between stitches and think it was a dropped stitch and carefully pick it up.
My advise. Calm down. And slow down. work on Knit Only at first and count your stitches after every row. Your yarn should always be behind your work for Garter (K all rows), so if you notice it's crept forward, stop and move it back behind your work and make certain you don't wrap it round the needle and create another stitch by accident (Been there, done that too!).
And most importantly have fun! who cares if your first couple of projects Grow/Shrink/Have Holes or Lumpy Bits. Soon enough you'll get better and they'll only be there when you want them to.