Don't be discouraged, remember this is a hobby and we are having fun!!
I am also a beginner and what I have learned is "unsewing" is a pain but the end result is worth the effort. It really helps to make sure your blocks are squared and the seams in each block are straight and in the right place. I have found if you ignore a little oops in a block, it is magnified when you piece everything together.
I use only the basic 24 x 6 1/2, 15 x 15 and 6 1/2 x 6 1/2 rulers.
Hope this helps and good luck with your next project.