Whether or not

After I put the saddle on, Zum stands perfectly still as I tighten the cinch. I don’t know whether or not I should get back up on Zum. My right arm is still very weak. Would I be able to handle riding Zum after he hasn’t been ridden for three months? I admit that after he bucked me off, I am afraid that he will buck me off again. I want to get over my fear. How can I do this safely?