Elevated AFP but no neural tube defects

Hi everyone. I’m currently 18 weeks pregnant. Last week I had bloodwork done that showed my AFP was at a 4.0 when average is 2.5. Because my numbers were high I had an ultrasound at the hospital on Friday. The doctor there said everything looked normal and he didn’t see any signs of a neural tube defect. My question is what happens now? I’m still worried about my results and no one has answers