Hello there. Thanks for writing. Fetal heart activity to appear so soon is a positive sign for pregnancy to be viable. However the finding of irregular sac might increase the likelihood of abortion when you have already started spotting. But you should not lose hope. I suggest you to get a repeat ultrasound after 2 weeks. In the mean time, you take proper bed rest. Avoid heavy exercise, weight lifting, stress and sexual intercourse. If you smoke or drink then kindly refrain. Take plenty of fluids with balanced diet along with regular intake of Folic acid vitamin tablet. Take care.