i think even a cock that is "hard-as-a-rock" is bendable and twistable to some amount. not much, but to some amount. so just because you can bend it a little, don't think you are not fully erected.
a good way to test your hardness is to pay attention how hard your dick gets during orgam. because shortly before ejaculation, your cock supposed to reach maximum stiffness. if there is a big difference between your "normally erect cock" and your "ejaculating cock", than you might want to talk to a doctor about it. there is nothing to be ashamed of, even guys at younger age may experience disturbance in their blood flow and its always the best to check out the "why" in time, because it might be a sign of another medical condition (diabetes, ...).
but i don't want you to get affraid now, thats pretty much the worst-case scenario i'm talking here about, its much more likely you have some other thing going on (e.g. the psychological pressure you put on yourself with "why-am-i-not-fully-hard-why-am-i-not-fully-hard-..." causes it, etc.)
so don't be affraid and talk to a doctor if you feel like you doesn't function as you're supposed to!