I'm an F-1 Visa student on OPT (this is first year of OPT)
I wasn't sure for my Federal returns whether to use 1040NR or 1040NR-EZ.
But, I already filed 1040NR-EZ while doing a standard deduction (Page 3,4 are blank)
And I filed my 8843 and my W2s
Should I amend it and re-file a 1040NR-EZ? Or is it okay?

I assume you are from India, since that is the ONLY country where the tax treaty allows F-1 students to claim the $6,350 standard deduction.

If that is the case, and you identified yourself as an Indian student on the F-1 visa on Form 8843, then the Form 1040NR-EZ is fine.