You certainly have the right philosophy towards creation, i'm glad you enjoyed making this. If you are unsatisfied with sketchbook, I would reccomend the app Procreate, its the closest experience to photoshop without the insane prices. The thing that sticks out to me with this piece is the perspective, although done on an intentional dutch angle, the ipad does not match with the angle of the table. This can be fixed in the future through sketching perspective lines in advance to help yourself. Nice work, keep drawing.