Have used these in the past, and they are designed so the canvas is very taught. From the first picture, it looks like the side rails are convex when viewed from the side. The rails should be straight, not angled so the middle of the cot is the highest point. Also, it looks like the canvas on the left side has wrinkles in it, indicating the fabric has to be slid to the left. As an indicator, the fabric located at the middle juncture should be right in the middle of the frame. Try sliding the fabric to the left,as viewed in the picture, then attach the end rail. Try attaching one end of the side rail to the end rail, then put very hard to attach the other side. Don't know if the material has been washed in the past, but it's also possible the fabric shrank. Try wetting the material, putting it together, then let it dry for a few days.