It doesn't matter if they are opposites. The Elements of Fire and Water go perfectly together. All elements (Air, Earth, Fire, and Water) may have difference; may have opposites, but they still work perfectly together. You can have more than one element as your "element" which you feel closely connected to. Though truth of the matter is that we all have each element within us. We all represent each element and thus have properties from each element.
Put it this way. We all have a specific Zodiac sign in which we are born under. That may make it our sign, but does that mean we represent the one only? No. Look at the meanings of each sign. We all have some aspect of each sign no matter how many or how few. They are all part of us; just like the elements are all part of us.
It's what we do with what we have that makes the difference. Work with them equally and you find balance and unity. You'll be equally connected to all. Work with specifics (not all) or just stay as you are and you'll continue with the imbalance that you have to where you feel connected to or or so, but not all of them. Work with the in harmony and discover the bliss of what they make when equal and unified.