Fear is only going to bring you down. It can take quite a while to be rid of an eating disorder, especially if it has been with you for a while, and no amount of relapses makes your recovery any less valid. It is a difficult fight, but you can do it. You’ll have good days and bad days. Just remember what you truly want. If recovery is your goal, you are already far along on your journey to a better life.
Bad days are inevitable, but you can pull through. Being afraid to slip back into your eating disorder can make you run closer to recovery, but if the fear becomes so great that one setback makes you doubt yourself, you need to recognize it and fight it.
Fear like this means you’re just waiting for your eating disorder to take hold of you again. It means you don’t think you can really get away from it. And in that case, you won’t.
We are all human and one setback does not negate all the hard work you put in up until that point. You aren't starting again at square one just because you had a setback. You are working towards something that is hard to achieve and it's only natural you will have slip-ups. If you recognize that you did something you didn't like, and feel bad over it, just get back on the road to recovery. That's all there is to it: putting a slip-up behind you. Many eating disordered people have relapses (sometimes multiple relapses) before they feel they are totally recovered. Just keep hopping back on the track to your goal.
Think of it this way: If you want to get from California to New York and you drive 1000 miles, then stop your car and therefore stop making progress, you don't have to start back at California to get on your way to New York again! You are still 1000 miles of the way there. You may have stopped and therefore your trip will take more time, but you don't have to start over. Just get back in the car and keep going. You'll get there eventually. And you can stop as many times as you want.