I think it's great to identify with any term that you feel applies to you.
I don't think anyone here will say that you can't call yourself poly unless you've actually been in love with two different people. Well, some might, but people say all kinds of things and I tend to just ignore the parts that sound stupid.
I think poly is half mental and half practical (ratios may vary). Some people just know, in their heart, that they are able to love more than one person at the same time. Others can't believe it until they wake up one day and found themselves doing it.
I've always known that monogamy is not for me. For the longest time, there was no reason to take it any further as I was young, single, and commitment-free.
I've also never been in two serious relationships at the same time. I've been in multiple romances at the same time, but nothing that I would call serious. I have a tendency in life that whenever I find something new and amazing in life, I throw myself into it wholeheartedly. Previous romances have been no different. As long as I was in the "honeymoon phase", I was so consumed by those romances that I had no immediate desire to be with anyone else. When I came out on the other side, it turned out that there was nothing substantial to maintain a longterm relationship, and things always fizzled out.
Wow I'm totally rambling. Anyway, my point is that if you feel you're poly and pansexual, then no one should object to calling yourself such!
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker