Chemistry Subject Test Prep Question

My student decided last night he wants to take the SAT Chem Subject Test on June 3, which is in a little over 3 weeks. What is the worst thing that can happen by taking it after waiting this late to prep for it? He is just finishing Honors Chem and has only taken a practice PSAT at his school. He sat and did one Chem subject practice test (College Board practice test) and struggled to get through it and scored a 680. If he wipes out on the Chem subject test in June, is there any way to suppress it so that colleges won’t see it when he goes to apply? And if he wants to take Chem subject test again in August to try to get a better score, will the better score be allowed to supersede the lower score? Do schools average subject tests? Also, I’m thinking about spending $875 for a souped up prep course (10 hours over 4 weekend-group sessions leading up to June 3). There are some holes in our school’s curriculum that need to be filled in along with learning the test flow and design and general strategies. For those of you who know the Chem test, is it realistic to think he can get his score up and do well by June 3? He also has regular school to contend with though finals do no start until June 12th.

Mine didn’t study at all and got a 700 after Chem honors. Her teacher said that was about normal for a student after one year, many take it after AP Chem, which is where you are seeing the higher scores.

I’m not sure I’d sink a ton of money or prep school in to one subject test.