I don't think you need to equivalent your +2 level courses.
Here are the steps you wanna consider:
1) Give TOEFL & SAT(Send the score directly to your college)
2) Fill out the application online at least couple of months before the deadline date
3) Make photocopies of your +2 transkripts. Go to your bank, have them all your photocopies attested. They will put stamp in your photocopies.
4) Open Mircosoft word document, type a letter to your college saying that Nepal do not have a system of sending transkript like in the US, therefore you are sending them the attested photocopies.
5) Fill out FAFSA to get financial aid.

Bank is just an example, you can go to any other government office like city hall to attest your photocopies. When you attest your photocopies, it makes it official. Colleges accepts official copies.

Regarding TOEFL & SAT: Most of the good universities require SAT. Check your college website in admission requirement tab. Some colleges don't require SAT. It depends on which university you are applying. Students who did their +2 from non-english speaking countries are usually required to take TOEFL. Check the admission criteria directly on the website of your college. All the necessary items are listed on the college website.

You mentioned it's been more than 10 years since you did your +2, I recommend you give TOEFL & SAT. It will be a good review for you.

Hello Sahara Koirala ,

After Reading your story, for a moment I remembered my position 5 months ago. May be My story is little different than yours but I hope this will atleast give you a little heads up about where to start from. I applied for the Grad program for Spring 2018 . The University asked for the WES evaluation like in your case and here what I did
1. I had Undergrad from T.U (7 years ago). So to get the Transkript Officially Stamped from
the Office of Controller (T.U in my case). I send my Undergrad Transkript and degrees to
Nepal via Fedex .
2. Here in US I browsed the WES site and paid some money to get the WES Reference #
3. My family back home with the received credentials and WES Ref # went to T.U and
processed the things to get the Officially Sealed Stamped Transkript in a envelop.
4. My Family send me that sealed Envelop as it was received from T.U.
5. After Receiving my package from Nepal I mailed it to WES .
6. After 2-3 Weeks WES completed their Evaluation and Send to my applied University .
7. University received the evaluation copy and they started their own processing.

This is my story hope this helps you!

Slightly different route as you are a PR: what about you join a community college now (no SAT and no ToEFL required, or you can enroll 3 cr. English to waive ToEFL requirement) and then transfer to a good school in fall. A DV winner relative bhai did the same in GA and moved to a good university in TX a year later. The CC accepted HSEB transkript after he went there to show them the original.

Just sent you the details by DM. Good luck!