It is probably due to intrauterine retained bits of conception that is incompletely evacuated by medication.
Therefore, post pill abortion
, one USG scan for lower abdomen is essential to check retained bits if any and may need to proceed D &C (surgical method) to complete the abortion. Consult with your doctor regarding this.
Practice safe sex
by using safe period/OCP/Condom etc to avoid unwanted pregnancy
& unnecessary vaginal bleeding. Be well.