I'm not sure I understand the problem you're having, exactly...
When you make a granny square, you should have more shells (groups of 3 dc stitches) in a round than you did in the previous round. The first will have 4 (one per side), the second will have 8 (two per side), the third will have 12 (3 per side), and so on.
The trick to making a really big granny square is to just keep adding rounds, and doing your 4 increases (or corners) in the same place each time.
The problem with making one big granny square, and this is true for any pattern worked in the round, is that the bigger you go, the longer a round will take to do.
Ok I see what I was doing I was counting my corners. it is working right. I feel like a total moron now. Thanks!