Testing for bacterial based STD's (chlamydia, gonorrhea) check for the actual presence of the bacterial agent; thus, testing can be done fairly quickly after the event.
Testing for viral based STD's (HSV, HIV, hepatitis) require at least a 3 month wait for antibody testing. The exception would be if you experience an outbreak of what you believe might be a herpes lesion which can then be swabbed for this particular virus.
Both these viral based diseases are most often tested through antibody testing (unless one would have an outbreak of herpes; then the actual lesion could be tested). The time period for this testing is 3 months after the event.
Again if her blood was not present, hepatitis B (or C for that matter) is not considered a risk.
Oral sex carries an EXTREMELY low risk of HIV transmission.
Think along the lines of .5 to 1 per 10,000 exposures with a source KNOWN to carry the virus. Your risk would be less since you cannot confirm this persons status.
Even if your penis bled from this scratch AND this woman was HIV positive, the risk would remain the same. Her saliva would not contain the virus. She would need to be actively bleeding from her mouth AND you would need to have an open (i.e., bleeding wound) on your penis at the time of the oral sex for there to even be a risk of transmission.
Keep in mind that in order for transmission to occur the virus must be able to actually enter your body.
If you remain concerned over this extremely small risk, either ask her to get tested or you get tested at the three month mark.
Perhaps an obvious suggestion considering your name.
However, he is 7 1/2 inches long and concerned he is "too small" when in reality he is larger in size than the average male and thus overly worried regarding his size. The issue may be more HER size than HIS.
I very much agree with FCL's response that he needs to ask her if she's satisfied before he starts worrying about such matters.