Take a look at the original sentence again:
Fighting the urge to crawl under her desk, Adriana looked at the
clock, there was still a half hour left
of class, more than enough time to do her poorly prepared, ten-minute speech.
You wanted to fix it this way:
Fighting the urge to crawl under her desk, Adriana looked at the
clock, so there was still a half hour left
of class, more than enough time to do her poorly prepared, ten-minute speech.
A comma with a coordinating conjunction like so is a perfectly legal way to correct a comma splice. However, you must choose a logical coordinating conjunction. So indicates result; it means the same thing as the transitional phrase as a result. Such a transition in the example above makes no sense.
You might want to consult the rules for fixing comma splices and fused sentences.
Go back to the sentence to try again.