The profit sharing contribution is a separate amount that is based on discretionary amounts the employer wants to put in the plan for the benefit of all the full time employees. It is allocated based on a percentage of salary and typically it is linked with a 401k plan.
The 20% withholding is required in most cases, but does not cover all of the tax liability for an early distribution. As example, if you are in the 15% tax bracket then there is still another 10% that will be due for the penalty at tax time.
You can find the tax rates for your taxable income at this hyperlink: 2017
Federal Tax Rate Schedules
