Yes, it is a high risk.
Make sure you test out to the 13th week from the date of the exposure.
Sex with out condom is dangerous.
Research says that while transmission can occur on the first exposure, it rarely does. It usually happens with repetative sexual encounters. That is not to say that it needs to work its way into you, it can happen the first time.
Statistics for transmission are: 1 chance in about 1000 exposures (female to male), and 1 chance in about 500 exposures (male to female).
We can not tell from your question how long after exposure you had the negative test. You'll need to follow Mike's instructions above.
Someone that has been recently infected has a high viral load and shed HIV in there pre-ejactulation and sperm at high volumes. Yes as Mike told you, your risk was HIGH and you need to test.