The fact that it settled down quite a lot may indicate not too much damage. I would suspect you may have given one of your menisci a minor injury. However you would need to get it checked out to be sure. I think if you can't get it straight then get it checked out. The physio can do a clinical examination of your knee which may indicate what is going on. A good examination doesn't give you 100% certainty about the diagnosis but it is a good start. They can also advise you on what to do to facilitate it settling down and healing. If there is a major problem there or there is some concern they can refer you on for imaging or and orthopaedic opinion.