When you first get the paper, it's good to open the packaging and let the paper acclimate to your environment. The paper is hydroscopic so will take on or "breathe" out moisture. Letting it acclimate will minimize this. That said, assuming the paper registered with no problems, it doesn't appear to be the issue.
It's also important to have circulating air in the studio.
To flatten, you can try using a blotter between the sheets (and possibly mist the back of the sheets) and put weights on the top of the stack.
I printed 10 colors.