20 year old female soft swollen lump on the medial inside of foot just below ankle joint is more defined when I flex. If I press on =no pain scared?

Skin lump. Many patients will get soft tissue cysts, bone spurs or even fatty deposits that all can be described as skin lumps. If you are concerned get an exam for the best diagnosis and treatment if needed. Best wishes!
It needs a look see. There are several possibilities, including a dilated vein or cyst. Have it evaluated by a foot specialist to better isolate the possibilities.