Concerned...

So last night I decided to try out my new breast pump since I heard nipple stimulation can help labor progress. I put both on my boobs and covered up. I figured I would just do it for like 10 minutes as long as I didn't experience any pain. Next thing I know I have liquid running down my stomach. I wasn't expected to actually get anything so I wasn't paying much attention to how I was holding the pumps. I had them on for maybe 5 minutes and this is what I got. I was shocked and so excited. My concern started tonight when I decided to pump for another 5-10 minutes and NOTHING would come out. If I squeezed my nipple with my fingers some fluid would come out

but it looked clear. I had the pump on each breast for about 10 minutes. Did I do something wrong? I'm terrified that I just messed my milk supply up or something. Any advice would be much appreciated.