Any kind of change to habitual thought is going to take practice.
If you think:
If I go over [insert weight here] I will have lost control and I will be unattractive.
Then everytime it occurs to you, think:
The number doesn’t matter, it doesn’t define me, I am just as beautiful as the ladies I admire, I can werq it too! :)
Besides practicing positive thoughts, try getting rid of the scale, don’t weigh yourself, and practice not comparing weights or body shapes. When you catch yourself comparing, remember that there is no reason to, for you there is no comparison, and if you constantly compare yourself to others, you will never be happy.