Congrats on finding SAI, it took me a while too and some friendly recommendations. I haven't been able to use it much yet and make anything to post on my account because my tablet broke . . . under curious circumstances. But good job, I really like it, I want to know what you used to make it look so . . . sketched/hand-drawn. But don't mind me, I'll just stick to my pencil and paper.
Sorry for belated reply. I'm not good with drawing and advices, but... All that you need is practice - it will make you more confident. Hard to draw long lines - draw with strokes. Try to find comfortable method. And real media, pencil and paper - that's even better. It disciplines you. You can erease and fix everything with tablet - that relaxes. Wrong way. Ugh. I will not wish you good luck, I wish you patience. Don't stop, keep drawing.