It is okay to skip ahead in your writing. If you think of a scene in your mind, go ahead and write it. That is what editing is for. You can type in a whole new document and paste it in when you get there, or you can just leave space and type in between. Often this can help because you can come back and fill in the gaps when your mind is freezing on one particular scene. Write the new scene. Then go back and write what leads up to the scene. Sometimes it’s a lot clearer later.