I am planning to give sat in this jan but thr is a problem that i havent started studying for it and i want atleast 1900 or 1900+ score what should i do is the time left enough for get prepared for 1900+ score ?
Step one: See if there's a seat for January. Usually Jan is filled up early and you'd be lucky to find one right now.
Step 2: Take a diagnostic test and see where you stand. Anything between 1800-1900 is a good starting point. Anything below 1650 is a cause of serious concern.
Step 3: Start studying! Diagnostic test showed you your weak spots. Rectify them. The key to a good score is 800 in Math. Oh and time yourself. Most people incl myself know the stuff but can't finish within time.
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Oh, and I think you should give it in March. Gives you margin for retake. If you're not giving AS then you can go for May/Jun with a potential retake in Oct.
P.S: IMHO if you have no clue about SAT and haven't studied yet, you certainly do not have enough time to score big in Jan.