A 28-year-old multiparous woman (G3P2) at 29 weeks of gestation is brought to the hospital with heavy vaginal bleeding (estimated 400 mL) and severe lower abdominal pain. On examination, she is anxious, BP 100/62, HR 110, RR 22. Uterus is tender and rigid. Speculum examination shows blood pooling in the vagina with no cervical lesion. Ultrasound confirms a placenta completely covering the internal cervical os with a large retroplacental clot. Fetal heart rate is 145 bpm. What is the most appropriate next step?