Drawing issue with graphics_draw_pixel


I gonna develop a doodle app both on iPhone and Pebble Watch. When draw on iPhone, I get all the point, and send the data to pebble and transfer the point data to GPoint. Finally, the drawing line will appear on pebble.

I use graphics_draw_pixel method to draw each pixel on watch, yes, it works fine. But only a little point move to different area on watch. That is not my expect. I want the last pixel I draw still at that position. How should I do?