As Loki says you can retake with no repercussion as far I am aware schools have done away with averaging scores.
As to the reading anxiety it is a different kind of test than what most undergrads are you used to. In undergrad you basically learn information and regurgitate it, but the LSAT, law school and the legal profession is not really regurgitating facts it is learning to analyze issues with a few facts quickly.
As an example gay marriage was a recent Supreme Court decision there is no dispute about the facts. The lawyers all agreed on who was involved in the lawsuit, what the issue was etc, the lawyers had on both sides had to use these facts and analyze them to create an argument.
Just as in a law school exam you will essentially be given a fact-pattern such as this. The exam Obama gave to his students at U of Chicago in 1996. http://lawprofessors.typepad.com/files/conlaw3.obama.1996.fall.pdf
. These facts are completely made up, but you will use what you learned in class to offer analysis to the questions. Reciting a list of the cases you read during the year or the facts of those cases on the test would result in an F. Instead in the first fact pattern involving a lesbian couples right to children and state action you will have to apply the 14th Amendment, fundamental right cases etc that you learned to the situation then do an IRAC, which will result in a conclusion either for or against the couple (you will not be marked down for saying they should have the kid or not you simply make an argument and reach a decision." My favorite quote from BarBri was that one of two lawyers in every case is wrong, but if you don't make an argument then your in trouble.
Then when you are an attorney a client will come to your office with a problem. Their problem is unlikely to fit any fact pattern you learned in law school, but you will hear their issue and apply the law as you know it. For example a client comes into your office saying the City will not let him do his Monthly Muslim Midnight marches through the residential neighborhood in the fictional City/State of Wazoo that Obama made up.
You will know Freedom of Religion exists, but you will also know there are time manner and place restrictions on the exercise of speech-religion etc along with a few other things I have long since forgot since Con-Law 2 I read Obama's Con-law 2 exam and now just realized how much I had forgotten : (
The point of all this is that law school and the legal profession is different. There is no "right answer" learning to obtain facts and analyze them very precisely is what the LSAT tests and it is not a fact driven test such where they ask questions with black & white answers. I.E. Who was the First President of the U.S. there is no debate on that question and that is the type of fact driven scenario most students are used to including myself before law school.
So you are right to be anxious it is a nerve wrecking test, but it is only the first step. Study, practice and do as well as you. Do not put unrealistic expectations on yourself I am sure I and everyone else on this board would love to see you get a 180 on it, but there is a 99% chance that is not going to happen. Instead you will study and I would your score will be somewhere between 150-160, which can get you into a number of law schools, but 99% of lawyers did not get a 180 or attend Harvard or Yale Law School so you have to be willing to accept that. Study your butt off get an LSAT score see what your options realistically are then make a decision to attend law school, forget law school, or retake the test, but step 1 is taking the first test.
I have seen so many people talk about law school and put off the LSAT and their life for years and now that I am 32 many of those people I went to undergrad with never ended up taking the LSAT let alone attending law school, but they put their lives on hold for 4-5 years thinking they weren't quite ready for the test. Meanwhile I took it and I did not set any records on the LSAT, but I did well enough to get into an ABA school with a solid scholarship and passed the bar first time. I am not a genius by any stretch of the imagination, but I took the steps necessary and didn't overthink the process. I hope you will do the same and wish you the best of luck.