I would put it on the frame and leave it sit that way for a bit. I've stitched with the creases in needlepoint canvas with no issues. The canvas will relax after working it for a bit. I would not steam at this point as it may distort the canvas. I would wait until the project is finished. After my needlepoint projects, I hand wash my finished canvas with dish detergent and roll in a towel to get excess water from the piece. Let air dry. I have a frame to square my work. After the piece is dry I do use steam to get it back to square on the frame. Let it dry again and then it is ready for framing/sewing.