why not try drawing out your picture lightly on the canvas first?

Acrylics do dry fast and can be painted over, to start out try using big A1 sheets of paper, just let loose, but do some research first , gather together some source material to work from, photos, drawings, cut outs from magazines.
Or start by using different materials - charcoals, pencils, watercolours, inks - changing from your usual materials might free you up a bit . Good Luck and remember you have to make many bad paintings before you can make good ones so don't put pressure on yourself to get it right from the get-go , learning from your 'mistakes' is the best way for an artist to learn, HAVE FUN!!!

Been there. I found that planning a painting out helps. I still get the jitters after i get my drawing on the canvas and the next step is to paint it, even more so when i'm working on a painting i've been hired to do. If it's a photo i am working from, i study it and make notes of things to keep in mind. These things help me do the hardest thing and that is, get started, because now i have a visual, mental, and written plan that helps me focus. I've been painting for about three years with oils but i use to work with acrylics. My art can be checked out at hellosanantonio.com under artist name ''Guerro''.