I know on the application, it says to report all grades no matter what, but my college counselor told me to not put the D grade of Precaclc (11th grade) I got into my application, as it was not a required class (of a-g) and that it will hurt me.(Is this true??) So I didn’t.
But now my friends are saying that I should have or the UCs and CalStates will think I did it on purpose to hide my grade for math that year and that I’m in trouble.
Should I email docs@applyucsupport.net to add in the information of this class and grade? Would it even help? I was just following what my counselor had told me, didn’t know it would have hurt me this much.
What should I do??
Pre-Calculus is an a-g course so it has to be reported. If you left off the grade and you are accepted to a UC or CSU, you will be required to submit your HS transcript. If the grades and courses do not match, then your acceptance will be rescinded.
Did you retake the class with a C or higher grade? For the CSU’s, if you repeat the class you only report the higher grade. For the UC’s, you report both the D and the repeat class grade.
If you did not repeat the class, you need to report that grade. For the CSU’s, you need to contact each campus and let them know of the mistake.
For the UC’s, you Email: ucinfo@applyUCsupport.net with the corrected information.
Keep any documentation you receive and I would also bring this up with your counselor since it sounds like they are giving wrong advice.
So should I email docs@applyucsupport.net to add in the info then? Or call them? Or is it too late for my UCs and CSU’s?? 
My brother had a grade reporting problem too but he appealed it and his appeal was accepted… I don’t know why my college counselor had told me it wasn’t part of a-g. And I couldn’t retake it because my school doesn’t allow me to retake classes unless it’s Algebra 2 or lower.
Use the email for the UC’s I gave you:
If you receive an offer of admission, be sure to confirm with the campus admission office that they are aware of the deficient grade or schedule changes. Although you must notify the campus of these changes, we cannot guarantee that a campus can go back to review an application after correspondence has been received. Make sure to save a copy of your correspondence just in case.
Email: ucinfo@applyUCsupport.net
Postal mail:
UC Application Center
P.O. Box 1432
Bakersfield, CA 93302
For the Cal states, you need to contact admissions at each campus individually. You might end up appealing so that is why I said to keep any documentation you receive back from the schools.
Ah sorry I just saw that, and I did email them immediately after my friend told me, but they just told me:
Hello ____!
Thanks for contacting the UC Application Center!
There is limited information that can be changed on your online application after it has been submitted. You must send your UC Application updates to us by email to the address provided below.
Make sure to include your full name, date of birth, and your UC application ID number. Any documentation beyond the body of your email, that includes the information above, must be in the form of an attachment. We will share your correspondence with each campus you applied to, but there will be no changes made to your physical application.
If you have any other questions please feel free to contact us again.
Thank you.
So there’s a chance that they will see it, but also a chance that they won’t see the changes, if I’m reading this right, right?
Since it is early in the application review process, they should see the update. Since your counselor steered you wrong, I would try to get them to upload your HS transcript with the correct grades and submit that for documentation or ask for an unofficial copy of the your HS and upload yourself.
If for any reason, the information does not make into your file, you keep all documentation in case you have to file an appeal.
Thank you for your answers so far, it really helps a lot! 
And my school is in winter break already until the 8th of January, so will that be too late to send a doc of my transcript in? Or should I just email them right now and just tell them I got the D grade in PreCalc class?
I would email them ASAP with the grade information. You can then submit a copy of your correct transcript once classes resume in January.
Okay, thank you, I will try this. 
Thank you for all your helpful answers!! Have a nice day/night.
Best of luck.