Hi Rhiannon! Pullovers do target the back, chest, and triceps so it is not unusual for you to feel it in your triceps. But when you do the move, you want to mentally focus on the back before you even move the weight to get a better back contraction. I also suggest remaining horizonal while doing this exercise.
Another thing you can try is different hand grips or different pieces of equipment with pullovers to see if you get a better contraction in your back muscle (ie: use a barbell, use a weight plate, use one dumbell in each hand, use one dummbell but hold it vertically instead of horizontally).
If after all that you still feel you are not getting an effective contraction, then select an entirely different back exercise to put in its place. You can do standing barbell rows with a 45 degree forward tilt(or hip hinge) before you go to the more advanced two arm flat back dumbbell rows. Good Luck!
