I know you just want to exercise the lines of your chest, shoulders and back, but the movement of lines also requires exercise and will also cause fat consumption. If you exercise too much on the chest and consume too much fat locally, and the main component of the chest is fat, it will easily cause a girl's flat chest, which is not a good choice for this girl.
If you insist, then I'll introduce you to the exercise of lines. You can choose to buy two lighter dumbbells, preferably adjustable ones. Lift dumbbells horizontally every day, keep your hands straight and don't control them too much. Try to control only the shoulder joint and let the dumbbell reach the height of the shoulder from low to high. Note that when doing this exercise, you must move slowly, not too fast. Only by moving slowly can you fully exercise without inertia. If you throw it too fast, you will not only get hurt easily, but also be inefficient because of inertia.
This kind of exercise can not only exercise shoulders, but also exercise chest muscles. You can do push-ups at this time. Don't underestimate push-ups. It's also hard. The lowest level is that you land on your knees and then do push-ups. Advanced ones can add weight and do push-ups handstand. Try to relax your shoulder blades when doing push-ups, which helps to exercise the lines of your back.
The sense of lines comes from muscles. As long as there is not too much fat, you can see some muscles a little, so the lines will be more beautiful. Of course, these actions are not enough. Those moves will make your muscles overextend. You need to do a lot of stretching so that your lines can be beautiful enough.
In addition, I can recommend you to do squats. Squat can't exercise the lines of shoulders and back, but it can exercise the waist, hips and legs, sexy waist and tight thighs and hips, which is the charm of a girl.