Hcg rising but not doubling

Hi, I had an ectopic last year and lost my right tube. December 24th I found out I was pregnant but have been having cramping low down and low back pains. They got me in for a Hcg test so on Monday (4w2d) it was 413 and on Wednesday today (4w4d) it was 638. They mentioned they’ll scan me next week but said they wanted it to double or rise by 60% however it’s only risen by 55% ish. Has anyone else had similar and if so what was the outcome? I just want to prepare myself 😫