When you go over onto the outside of you ankle (which I presume is what you did) you can damage ligaments and muscles that stabilise the ankle. The ligaments on the outside of the ankle have a lot of proprioceptive (balance) receptors. If you damage the ligament you can affect your balance which then leaves you at risk of further injury. The muscles that run around the lateral ankle bone are used so that if you start ot go over on your ankle then the proprioceptors recognise this and then recruit the muscles to put your ankle back to neutral. If these are damaged or weak then they may not be able to neutralise the ankle.

To fix the problem you need to do some balance exercises - standing on one leg. You should be able to do this without putting your foot down for at least 30 secs. Then when you can do that close your eyes and stand on one leg (obviously stand near something you can hold onto if you start to fall). The second thing is to strngthen the muscles. The basic exercise would be cross you feet (bad one on top) and then push your feet into each other as if you are trying to turn them out. After this you need some resistance training doing that action. I use theraband which you can get from a physio clinic.

Hope that helps