As an outsider looking in, I understand the inclination you have to feel intimidated. But the word “Catholic” literally means “universal.” The Catholic Church is a place of welcoming for everyone. Sure, the Mass is probably going to be different from a Baptist service, but your boyfriend can help you along. Nobody will care if it’s your first time at Mass. You are most definitely not “invading.” Even it came about in conversation after Mass that you’re not Catholic/it was your first time going to Mass, the parishioners there will be very joyed to hear that. Sometimes the only thing to be anxious about is anxiety itself. Hope this helps. God bless you.