Scared to orgasm

Me and my boyfriend are starting to become intimate and it’s my first experience with anything sexual. When he fingers me, I enjoy it and I can feel myself getting close and reaching climax however it eventually just becomes too much to the point where i want him to stop. I realised I get too overwhelmed as I can feel the sensation in my legs and stomach and I don’t enjoy it as much. I realised the issue might be because I’m being to uptight so I tried to let go and relax and let him continue but it eventually got too much once again. Can anyone give any tips?