It sounds like you sewed the strips all the same direction instead of alternating or possibly ironed instead of pressed your rows. Also, if the fabric wasn't pre-washed &/or starched and on the thin side--it will stretch & warp when a hot iron touches it or some of the really thin stuff--just by handling it too much.
So--point #1 would be did you prewash & starch your fabric before you cut it especially if it was the thinner stuff?
Point #2: Did you alternate sides when sewing the strips together?
Point #3: Did you press (not iron) the seams all the same?
Point #4: Are you having trouble with the ruler slipping so that your blocks are out of square when you subcut the strips?
Are you a new quilter?
How accurate or at least consistent is your seam allowance?
Don't give up. Maybe today was just not meant to be a sewing day.