Embryo grading

So I have three 5 day frozen embryos and there are two 4AB’s and one 4BB. I go in Thursday for a sonogram to check my lining and also my ovulation so that we can schedule my FET. I’m 38 years old so my doctor recommended that we transfer 2. I’m wondering which two would he transfer? The best ones? If those fail my chances to get a baby from the 4BB aren’t as high as the 4AB’s so I’m a little concerned. I don’t have any money to try and do this whole process again so I’m praying to get at least 1. Anybody have a similar experience? Backstory is I had my tubes tied and then a failed tubal reversal. I ovulate regularly and my cycles run like clockwork. I just don’t have the tubes available for conception. We’re doing a natural cycle IVF which is no hormones since I don’t have any fertility issues according to my labs other than my tubes. I took Clomid for 5 days and was able to retrieve 6 eggs that all fertilized. Only 3 made it to 5 day blast and freezing.