M three months out of acl reconstruction surgery and bi menisci repair , i have only 100 degree of flexion and i haven't got the full extension yet?

Hopefully that: is better than when you started. Most of the benefits would be there by 3 months, AND, even without having a problem and surgery, people can improve their mobility, strength and flexibility over time with consistent physical activity. Signs of problems would be deformity, swelling, things getting worse not better over time, or signs of infection.