If there was only 1 Sim that you were stuck on, then you're fine. 1 Sim is not going to kill you and chances are, it was probably a pre-test one.
Since there are 6 Sims on REG with one being a pre-test, only 5 will be counted. Each Sim is worth 1/5 of the 40 points. So each Sim is worth about 8 points. And they grade each Sim based on the number of boxes you have to answer. So, let's say you had one Sim on MACRS depreciation. On this Sim, let's say there were 8 questions asking you to calculate the depreciation. Each box is worth one-eighth of that Sim. If you get only 4 questions out of the 8 correct, you'll get around 4 points out of the 8. You don't have to get an entire Sim right to get points.
And it also could be (although it's never been proven) that each particular question is weighted based on difficulty. We don't really know for sure. The AICPA has this whole secret grading system. But one thing I know for sure is that there IS partial credit on a Sim. If you get only 4 of the 8 boxes on TB Sim #1 correct, then you'll get points for those 4 questions you got correct. Trust me, if they required you to get all questions in one SIm correct, then these exams would only have a less than 10% pass rate, lol.
Don't worry. I'm sure you did fine. if you got an 87% on the practice test, then you'll be fine. Most people do better on the real exam.