Special Lesson #1: Oh no! My story got turned around! What do I do?

Before I start this lesson, I would like to give a huge apology for not updating since July! I started high school this year so I'm still transitioning and I haven't had time for writing. I am sorry everyone, I really am.

However, it's Christmas break, and I am ready to go!

So I remember getting this comment back during the summer;

And I knew how easily that could happen; it had happened to me mulitple times before.

So first off, I will help explain how to prevent your story from getting turned around in the first place, and then I will do my best to give tips on what to do when it does.

So, how can I stop my story from going the wrong way? 
As I have mentioned before, plan your story out. I know that this isn't going to ensure it 100%, but it will help you know where you want your story to go. Now you don't have to know exactly how many chapters you want and how long they are going to be, but even just having a simple chapter layout would help.

For example, this is a layout that a friend and I made for a story that we never actually did.

Prolouge; Day they met in preschool
1; A day of school, describing
2; Liam gets a pain, more describing
3; Liam collapses, random filler crap
4; Niall makes liam see the doctor
5; Liam ends up in the hospital, he could die
6; Filler
7; Niall watches the video
8; Filler
9; Liam is all better yay! 
10; Drunk driver
11; Grieving
12; More grieving
13; Romeoing
 

Yes it's for a One Direction thing go away.

So as you can see, it's not like we have every detail planned out, we just wrote down the general events of each chapter so that we would know what each chapter should revolve around.

Also, you could write your entire story before posting it (which is what I do and that's why I have 30+ fanfics sitting in my folder...).

Now if you did that and you posted a chapter and kind of had an "Oh crap!" moment and realized that this isn't exactly how you wanted your story to go, you have a few options here, so don't panic! at the disco just yet.

The easiest would to be to just delete the chapter and give a small explantion (if it's on a website like AFF, FFO, Live Journal, etc), because your readers are more than likely to understand.

Or, you could work it into your story, and this might be very hard. I would know, don't worry. But as a dedicated writer, you can work around the mishap. Look at your plot line, and try and find where it got screwed up. Why and how did it get turned around? Did you accidentally kill an important character? Did a pairing break up that wasn't supposed to? Well, it happens. 
I can't really give too much advice on this other than have faith in your writing abilities and sit down and just think. You can work around it!