Why? I work as a private college consultant, and I would not advise that, nor would I advise to retake a 780 Literature test. Far better you should beef up the rigor of your curriculum. Your test scores are terrific! I’m not sure who’s giving you advice. I’m also guessing you are a URM. Your test scores are very, very strong for any candidate, and particularly for someone in an underrepresented group.
My oldest son was a URM and had a 730 on the Lit. No way did he retake. He got into all his schools including a couple of Ivies and MIT. My middle son, not a URM, got a 710 on the Lit. No way did he retake. He got into an Ivy. No reason to retake your fine scores.
And you can just submit the ACT score and leave off the SAT. Absolutely zero reason to retake it even if you have a low writing score on ACT.
I would definitely encourage you to take hard courses; go for higher level math-up to Calculus maybe, and AP Level Lit with such a strong Lit subject test. If you want to take college classes, take calculus and some freshman English lit or AP lit.
Not sure who’s giving you advice, but it seems a bit off to me. But that’s just me! 
BTW, if you have good essays and you and/or your counselor can write about why you want to graduate early, that may help soften admissions towards your weaker course rigor. Make it good!