Yes. You are not used to stretching your throat open that wide while you sing. You can back off a little if it's feeling sore. Sore is OK when it's like the good sore you feel after an athletic workout. Sore like real pain or a strain is NOT OK. You just want to learn to make an open throat posture that feels natural and right. When you do, it will also SOUND natural and right.
Monitor yourself and find a balance between total relaxation and ensuring your vocal tract is an unobstructed, Open Tube.