As CanIMakeIt said, 99 is not a percentile. After all, the passing score on Step 1 is a 2-digit 75. If that were a percentile, that would mean that 75% of test-takers fail Step 1. This is obviously not the case. The two-digit score is an artificial construct pegged at PASS = 75 to satisfy the wording of certain state licensing legislation (see USMLE website).
Other than that, it is impossible to assess your chances given the information you provide. You can easily look up
Charting Outcomes in the Match for 2007 and find that
(a) a 237 is approximately at the 75th percentile for independent applicants who matched in general surgery in 2007
(b) of the 78 independent applicants who applied to general surgery in 2007 with a Step 1 score between 231 and 240, 57% matched. So even with this score,
based on the score alone, you have a slightly better than even chance of matching. Of course, Step 1 is a very small part of your application. Do you have US letters of recommendation? US clinical experience? Are you able to effectively communicate in spoken English? These will all be important factors in your application.
I cannot imagine that I am the first person to provide this information on SDN. The information provided above is such that you could have found and evaluated it yourself.
So I can't honestly claim to have given you any information you couldn't already have known.