Your risk would be, at the most (assuming she was HIV positive) extremely short term exposure from the torn condom. However, since you immediately withdrew it is highly, highly unlikely that there was any risk whatsoever.
If you want the statistical risk (and many ask about this), the stats we use for unprotected insertive (you) anal intercourse is 6.5 per 10,000 exposures with a source KNOWN to carry the virus. This is assuming that the act was carried to completion and that your penis would have remained in the anal canal unprotected for quite a bit longer than it did.
So....in terms of stats...your risk would be less than what I quoted above because...1. the unprotected contact was, from what you describe, extremely short and 2. you cannot confirm your partners status.
You are also correct that your sore throat the next morning has nothing to do with HIV symptoms. The first symptoms of HIV occur two to six weeks after transmission, not the next day.
The recommended time period for testing is 90 days after a potential exposure. Screening tests look for antibodies the immune system begins to produce after transmission has taken place. By 90 days 99.9 percent of newly infected folks will have enough antibodies present to be picked up by current testing methods. However, most folks just can't wait that long. If they do their first test one month after a potential exposure, we use the statistic that 95% of newly infected folks will have enough antibodies present to be picked up by current testing methods. Thus, some will test at one month and retest at three months.
Another option is to have your partner test. If her last partner prior to you was at least 90 days and she tests negative, she, of course, does not have the virus to pass on to you.
I hope this makes sense.
Gail