What you can do at this stage is press down the creases firmly. You can use the ruler for this and slide the edge of the ruler across the crease causing it to press down firmly.
Sometimes I would add a small bit of blue tack to the front tip to give it weight to fly harder.

You can turn up the wing tips to get more height.
Some people fold the wings or fuselage in half making it smaller.

You can paint, colour your paper plane for a more personal look. Enjoy. More to come.

All the best from
James M Sandbrook.

6th of April, 2021.