Help! How do I ride a large penis?

I have been seeing this guy for almost two months and we’re starting to have sex regularly. He has an abnormally large penis in length and girth. By far the biggest I have ever worked with. I am normally very confident in the bedroom and have always felt like I was pretty good on top. But I am struggling with how to maneuver. It’s not painful, but mobility is an issue. It’s just going very smoothly. And of course his favorite position is when the woman is on top. I feel like I am not pleasing him. He hardly ever ejaculates and it’s giving me terrible sex anxiety. When we start to get in the moment I panic. If anyone has any tips or tricks for me to apply in the bedroom It would greatly appreciate it.