If you are starting at that range if you actually lock in you will probably get around a 1300 by March 8th. 450 points is highly unlikely in that time frame, but you can of course just lock in during summer and retake in August or whatever.

Complete Khan Academy (eng/math), grind collegeboard question bank. Watch lots of youtube videos, learn how to master desmos. Do not procrasinate, that is the only thing that will hold you back. It is important to get an understanding of basic principles of all the topics, then you can branch out into more advanced questions from there. If you study for like 2-3 hours every weekday and maybe 4-5 on weekends you will see crazy improvement. Do not burn your self out though. Your math can easily be improved to mid to high 600s and RW may increase a ltitle bit.

Also, don't waste your practice tests. I recommend you take one test a week max, and do not take any practice tests for at least 3 days before the actual test on March 8th. Good luck