Most left-handed people I know turn the page at an angle (which differs between individuals) that allows their left hand to slide above or below the line they just wrote.
This certainly needs some getting used to, but doesn't seem too unusual, considering one of my right-handed friends writes with the paper lying at a 90° angle to him.
The most important thing to keep in mind is that you need to sit and write comfortably. Otherwise you'll get exhaused or cramped up whenever you need to write a lot of text (like during an exam) and in the worst case get back or shoulder pain. Therefore I suggest trying to find a comfortable posture that puts the hand below the written line. I you put your hand above the written line, you have to curl your whole upper body into a kind of spiral that has your writing hand in it's center. I have a friend who managed school like that, but always felt exhausted and stiff after writing long texts.
You should take some time to experiment. Lay the paper at whatever angle you'd like to try and write 2 lines. Then angle the paper to the left or right and repeat the same 2 lines. Have a look at this video at 1:45 minutes. There are many more videos of left-handed calligraphers explaining how they hold the pen and position the paper.