1996 Pontiac Grand Am Clutch

I just purchased this car a few days ago. It drove great, shifted smooth. I was doing fluid checks and noticed the clutch fluid was really low. The cap said to use Dot-3 brake fluid. Never having owned a manual before I was unsure of this. I went to Wal-mart automotive center and they confirmed it. So I put in the brake fluid. This was yesterday. I went to drive it today and the clutch pedal was all the way to the floor. I cannot get the clutch to release. I can pull the pedal up to me but the slightest pressure causes the spring to pull the pedal back to the floor. Wal-mart technicians told me I used synthetic brake fluid in a non-synthetic clutch. I've never heard of either. Any ideas?