Thank you for asking your query.
From your description I understand that you assumed that your pregnancy to be 5 weeks old, but now concerned it is more than 5 weeks, because you are not sure about the last menstrual period, whether it was menstrual bleeding at all.
Now even in that case, I should say the gestational age is corresponding to the ultrasound. Heart beats are usually visible only by 7-8 weeks of pregnancy. A discrepancy of one or two weeks may be considered within normal limits. So your ultrasound is more or less on ‘target’ and there is no need for any concern regarding that as of now.
I understand that you have been exposed to alchol, xray, physical strain, drugs etc during early pregnancy. While these are considered risky and bad for the growing fetus it’s not necessary that it should do some damage always. Most of the time the baby will be safe and you just need to take precautions here after. Incase you do not want to continue with the pregnancy I recommend you to go ahead and discuss it with your Doctor (Ofcourse as per your religious / ethical and legal views). You should decide, after discussion with your partner whether you should go ahead with the pregnancy and then take an informed decision.
Hope this helps.