Hey CAAS,
I forget that the Postcard is a 3D effect and is only available in extended versions of Photoshop. So, if you don't have an extended version then this won't help much. I actually tried a postcard from your image and since I did not have the original psd it did not turn out well.
Are you using the Pen Tool or the Poly Lasso Tool? You should be using the Pen tool. Using the pen tool eliminates the need to "draw". It's just about clicking a point and then dragging to get the right curve, no drawing required.
I did make a version with a tilt (command + T > rotate) and a rather dramatic backlight to demonstrate what I was talking about in my previous post.