Will I use everything I learned as a Math major in the workforce?

You will go to school and learn to look at problems in a particular way based on your schooling. You actual use of math will likely be minimal or vary applied to particular situations. This is a big lesson that most graduates of STEM careers need to realize. You will apply your knowledge but likely will not be dealing with your text book theory on a day to day basis. It was a shock for me on my first job.

The future is based on Maths. The Data is the new universal unit all the businesses will need to be able to analyse otherwise they'll die.

At the workplace, while you are not going to be spending time solving equations and graphing functions in the workplace, you are going to use the critical thinking gained through taking math and other subjects to solve various challenges that you will face as part of your daily work tasks.
As far as been an expert in math, I would say practice makes perfect. I would suggest doing more problems and not looking at the answers until you try multiple times! Also, if you can find someone to teach what you have learned to, that will help you master the topic.
Hope this helps, Thanks!
~Hakim