Beta question

Arly • Expecting our baby 🎀 May 2018
So I had my 1st Beta on Friday which was 9dp5dt which was 50 and then my 2nd beta yesterday which was 88. My doctor wants me to go back tomorrow to ensure it is still rising. He said it could be that I'm a slow riser or implanted a wee bit later. Has anyone experienced this and had a successful pregnancy?