My self employment tax was already calculated into my quarterly tax payments, do I need to file for schedule SE or no?....

Im a independent contractor for a call center, so the whole year of 2018 I used a site to help with my withholdings(quarterly tax payments). on this site, their calculator for figuring out the withholding percentage also includes the self employment tax( medicare and social security) as well as federal tax rate and state tax rate. so this gave me my percentage of whitiholdings to take out of my income everytime I got paid. I'm just now becoming aware of schedule SE, so im freaking out a bit because I've been sending my quarterly payments to the irs which included the self employment tax. so do I need to file a schedule SE, or just submit my withholding quarterly taxes?