Fontan heart and pregnancy

I have a Fontan heart due to a number of CHD's. HLHS, TGA, PA and TA. I've just discovered that I am 5 weeks pregnant and I have already had my ultrasound scan which was good, embryo size was normal. No concerns there yet. I have a cardiac ultrasound booked in a couple of days but I am feeling fine in myself. Just completely terrified as this is deemed a 'high risk' pregnancy. Looking for any and all advice from anyone who has been in my position. Thank you.