Drawing Practice

I won't be back at the MAG for a whole two weeks since my next class is on the 24th. Today I decided to paint something that I will draw first. When it comes to picking something I want to paint/draw, I get so indecisive. I want to do it all, which makes it so hard for me to do. For my next piece, I will be painting a goldfish. I already started drawing it, I will most likely finish drawing and painting it all today. I find that when I put a piece to the side, it becomes harder for me to finish I'm not sure why.