Is it possible to have an ectopic pregnancy if the hCG levels for a two-day increase are less than double?

Hello doctor,

I am five weeks and four days pregnant since my last menstrual period and have had positive home pregnancy tests for one week. My hCG levels were 308 mIU/mL a few days before that. The blood test was repeated 46 hours later (not full 48 hours), and the results were 467.7 mIU/mL. Using an online calculator, I determined that was a two-day increase of 54 percent and a doubling time of 76.21 hours. I know that is low for a successful intrauterine pregnancy. I am going in tomorrow for further hCG testing. I want to prepare myself. Is it highly unlikely this will be a viable pregnancy? The doctor said anything more than a 30 percent increase is fine, but from what I read online in medical journals, anything less than a true doubling indicates non-viability. Should I be worried about ectopic pregnancy? I have tender breasts, but that is my only pregnancy symptom (no period or bleeding). I conceived using intrauterine insemination. The fertility medications I used were Ovidrel trigger shots which I did two weeks back, and then I conceived two days later. Do you think there is a chance this will be a successful pregnancy, or do you think I should be preparing myself for a miscarriage or ectopic?