That so-called extra test is a joke and has no practical significance. Is to let you sketch and draw geometric plaster. Few people failed in that exam. So don't be nervous at all.
It's right to learn sketch, and you can also learn watercolor. There will be a sketch and watercolor course in freshman year, so don't worry. You can buy some hand-drawn books on markers and copy them. In fact, urban planning and architecture are exactly the same as freshmen and sophomores. You can buy hand-painted paintings and calligraphy on buildings, so you will be much better than others. After drawing, hand-drawing is mostly done with markers.