Uy, this really needs a doctor's check, ha, hindi safe na mag-assume pa lang based sa PT at ultrasound findings alone, kaya please go back to your OB para sa proper evaluation and follow-up.
Four days delayed with a negative test can mean maraming things, pero ang thickened endometrium na nakita nila needs professional interpretation, one of my mum friends had similar situation at kailangan ng repeat ultrasound after a few days para ma-clarify. Kaya please don't stress yourself muna, just get that follow-up appointment scheduled ASAP so your doctor can monitor kung ano talaga ang nangyayari. Malalagpas yan, pero kailangan ng tamang guidance from your OB. Sending you strength!