I have an extensive stash of fabric that is over 3000 yards right now.At one time it was twice this size. Several things happened along my quilting career that caused my stash to expand in giant leaps. At first because I was not following any pattern I would guess just how much fabric I thought I was going to need. It seemed I always had more than I needed. Then I would see a fabric on sale that I thought would look good in a quilt one or two ahead of what I was already working on and would buy that. It stayed pretty level until a JAF near me was closing shop as well as a Hancock Fabric. When I was able to get fabrics at 80-90% off I was getting everything in sight and coordinating one quilt on top of another until I was a good 20-30 quilts ahead of my current quilt. Oh my I realized I was becoming a quiltaholic. When we moved into my new home here in Waterford DH built me in the best sewing studio ever with a big cabinet just for my stash. Of course I wanted to fill it but I was still doing well and had empty shelves and only about 1/4 was filled. Then the big day came where I was let in on a llittle secret. A woman had passed away and she literally hoarded fabrics. She had 2 large bedrooms floor to ceiling and rows of shelves and built ins full of fabric. Her daughter sold it to me at $10 a large black garbage bag. I spent $200 on some of the most beautiful fabrics ever. Some was still in coordinating 5 pieces pieces and in the bag from the LQS! By the time I got it all washed and pressed and put away my once lightly filled cabinet was almost full. I try to work from my stash most of the time but found that I would still buy new fabrics on sale a great deal. Then I stopped going to the LQS and JAF unless I needed something important. Now I purchase online and I only do that if I can't find what I need in my stash.
I seperate fabrics by yardage. 1,2,and 3 yard pieces and coordinate by colors and lay in the cupboard as flat folds.
I have a second upper cabinet that is 1/2yd and fq's. I then have 3 seperate bins for scraps.
Last fall I ran into an exceptional sale at JAF that blew me out of the moratorium for a bit when I bought fabrics for 1 penny a yard. I bought 140 yds of fabric for $1.40! Now I have fabrics stacked under a workbench and in boxes. There is also fabric under beds and in cedar chest. I do donate fabrics to charity groups from time to time. My stash will out live me 3x's I'm afraid but I do know it will go to good use in a quilt someday. Friends and family make frequent stash raids and it brings a smile to my face.
The best way to prevent this from happening to you is by doing what you are currently doing. Buy only what you need for a quilt always being sure you buy just a bit more than a pattern calls for just in case of a mistake. Save your scraps for scrappy quilts and don't get started buying extra fabrics. I have put a lot of $$ into my stash over the last 30+ years and have no regrets and I have never put fabric before family or bills even though I know I am a fabricaholic.