Thank you for asking your query at DoctorSpring.
The ultrasound is probably early in your case. A normal ultrasound can detect a pregnancy only after 4-5 weeks from ovulation. (A transvaginal ultrasound can detect it a week earlier). However urine pregnancy test can be positive even earlier.
So I would recommend a repeat ultrasound scan after 5 weeks of the sexual act.
I would like to know when (1) was you partners last menstrual period was, (2) her regular menstrual cycle duration. Also (3)when did you do the Urine test and (4) pregnancy test and (5) when was the sexual intercourse . With these details I might be able to provide a more accurate prediction.
You can reply as a followup question.