First, you have made good fabric choices. Just keep in mind that each strip should go the way you have on the strips you joined, right leaning diamond, triangle, left leaning diamond, repeat. As Kristakz said, the cutting and seam allowances need to be exact for this to work.
If you are not comfortable doing that RIGHT NOW, do another project and come back to this one. I am not suggesting giving up on it, merely postponing it until you have a few more projects 'under your belt'. Recently, I tried an 'impossible' UFO and found it was NOW really easy for me.