Tips to keep Trikonasana from being a pain in the neck.
Check Your Curve
To put the correct neck curve into Trikonasana, come back to your wall setup and tip your pelvis to the right to come into the pose. Lengthen your spine from your lower back out through the crown of the head, so your neck decompresses along the midline of your torso. Check that the back of your rib cage and the backs of your shoulders are near the wall. As you also bring the back of your head toward the wall, make sure that you don't stick your chin out (thus hyperextending your neck) or tuck your chin into your chest (flattening the neck). Check the curve with your left hand.
Now you're finally ready to turn your head to look up at the top hand. Just remember that if your head is forward or your neck is sidebending, flat, or hyperextended, your neck rotation will be limited or even painful. You may want to ask for feedback from your teacher or an experienced friend to make sure that as you turn your head, you don't stick your chin out, bring your chin too close to your chest, or tip your head up.