I have mild recurrent pain with tenderness in the distal end of femur that hurt me when I bend my knee and walk...Is it osteosarcoma? Cause I'm scared

Unlikely. Osteosarcoma is beyond rare but the easiest way to allay your fears is to have the leg examined and x rays done.
Pain. You need a full workup. A MRI would show a sarcoma. Unless you have a family history of sarcoma, the risk is low, but you should still be worked up.