The fact you were worried for him shows you are a great mum. You are letting him explore and learn the consequences of certain explorations. Just think how many cuts bruises they are going to get as they grow older, you can't wrap them in cotton wool. You should have seen the panic attack i had when my boy fell off the sofa and banged his head (had a 5p size bruise and has decided he doesn't like that sofa anymore but otherwise perfectly fine). I felt like such a bad mum for not keeping a closer eye on him but didn't know he would pick that day to finally prove he can roll by himself.
The fact that you feel the way you're feeling shows you are not a "shitty mother" you sound like a very caring, loving mumma! It's so quick for little ones to get bumps and bruises once they start moving around, I had an incident with my first and felt so bad so I understand how you're feeling x