What are the chances of miscarriage after seeing a heartbeat of 131 at 6 weeks 5 days when the embryo isn't growing properly only at 6 weeks 2 days?

Low. Actually a fetal pole measuring 6 weeks 2 days when you are 6 weeks 5 days pregnant is fine. Babies come in all sizes -plus or minus 5 days measurement (ahead or behind) is fine. Also not everyone has 28 day cycles and if you did not ovulate on day 14 of your cycle, dates may be measuring a little off. Were you told this was abnormal, because I do not think it is, unless i missing facts.