lynbrown, not really enough info here (and I am a retired occupational therapist, not a physio) .How do you think you did it and has anything like it happened before? any heat or redness; achey pain? toothache pain? sore pain? I am assuming that the pain is in the crook of your knee? Is there any joint instability? Does the knee give way at all?
Basic advice is not to do what hurts it for the moment. Go upstairs one step at a time leading with the good leg and downstairs leading with the bad leg. Take your preferred pain relief and use an icepack (frozen peas in a pillowcase) to rest the slightly bent knee on when seated. Best to elevate the leg and keep is slightly bent if possible. If this treatment improves it by monday then its minor, if it gets worse, or if at any time, the leg gets hot red and swollen, then get yourself to the doc. Don't put bandages or supports on it.