advice needed following ORIF

I am a 62 year old female. I fell down the last 3-4 stairs a month ago and had comminuted fractures to both tibia and fibula. I had surgery to insert a plate on the fibia on July 9th. I am normally an active person and my hobby is long distance walking. I know I won't be referred to a physiotherapist until my cast comes off but what exercise is it safe for me to be doing at then moment? I have a short leg cast up to the knee.
I have been doing abdominal curls, leg raises and cycling in the air. Will I do any damage to my leg? It doesn't cause any pain.
Thanks in advance:)