Colleges won't see that you got an 8 on the essay unless you send that particular set of scores to them. NMSC doesn't forward any reported scores to colleges, they just check to see that you have achieved a "validating" score. If you want to re-take the SAT to increase your chances of receiving merit scholarships outside of the NM pool go right ahead, but you shouldn't need to re-take it for advancement to NMF status.
To make extra sure, double check your 2100 as a "validating" score using NMSC's formula. You need to check your score details on the College Board website to find your multiple choice sub-score on the writing section, and multiply that number by 10. Then add in your M+CR score (1380 in your case) and make sure the total exceeds 1960, which is NMSC's cutoff for a "validating" SAT score. In your case, you would need to have a multiple choice sub-score on the Writing section of at least 58. Since you feel that your essay brought down your overall Writing score, I'm assuming you'll have no problems using your current score. Good Luck!!