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I am sorry. I haven't heard of any medical condition referred as tensing up. Perhaps the technician just meant that you are tensed and nothing such as pregnancy
It would also not be possible to know whether or not a person had sexual intercourse a day or two before sexual intercourse. And sexual intercourse does not have any relation with the results of the ultrasound
In most possibilities, it seems the scan did not reveal a pregnancy. You should be able to get a written report of the ultrasound scan very soon, which will confirm about the scan. So my suggestions are not to worry about what the technician said and wait till the formal report is announced.
Hope this answers your query.