Incomplete Bladder Emptying?

Hi. I have had the typical issues for the second time in a few months but this time I developed the feeling of my bladder not emptying completely and slight tension in my bladder upto an hour after peeing. My post- void bladder urine was 60 ML, although the doctor took 10-12 minutes between emptying and measuring the volume. He told me 60 ML is perfectly normal. I am not sure if it is normal then why am I getting the feeling of my bladder not emptying properly. Can anyone help?