I only bled lightly and passed a medium sized clot within 24 hours while on misoprostol. did it fail? how do i know if it's successful?

You may or may not be successful. The quickest way will be ultrasound of the uterus which can give you an answer right away. Blood test weekly for 2 weeks, HCG level should be lower with the second test with successful abortion or you are still pregnant if the level keeps going up. Last option: urine pregnancy test 2 months later, test should be negative by then if the abortion was successful.