Hello arianagupta2001,
It's difficult to find motivation within oneself I am dealing with obstacles myself trying to find and push what you know and what you can achieve.

Set you goals smaller so that you can achieve to build confidence and also make you motivated.

This means take 5-15 minutes a day studying in a quiet place and watching videos. First off also stay with one topic only. It's easy to do reading and quickly switch to math but this does not always help instead set your Goals on a day to day mission for example,

Monday - Study SAT Math
Tuesday - Study Reading

Finally look at your data where are you weakest at to which points do I need to work harder?

Once you gain the goals you've reach then award your self something small whether watching your favorite movie, eating chocolate or favourite dessert or buy yourself somthing small as when you reward yourself then it Motivates you even further.

Take things slowly and don't rush things it's to easy to study hours only to be frustrated.

I believe your going to do this and accomplish the goals within you but Motivation is something within you that you have to believe you will pass the test as Fear is mine and others worst enemies it creates a bug that says I'm not smart look at the Winter 2018 Olympics as the athletes didn't reach this far because of having Talent they had failed many times before reaching that gold what was there motivation?

Picking themselves up and starting again you need to do the same so you miss or have troubles with the subject then just take a break then get up and say to yourself " I will do this " even if it's still hard to do remember there are always second chances to take the SAT again.

I fell flat on my feet many times, had many challenges and yet to this day I learned I got further by falling then looking up at the sky because once you pick youself up and see the sky your even more amazed by the beauty of it and appreciate it more.