Since you did not write "Exempt" on your W-4, has your employer been withholding federal income tax from your pay?
Filing your tax return for 2019 will resolve the problem. Depending on how much you make, you might be glad that you didn't write "Exempt."
I assume you are single, under 65 years old, not blind, no one can claim you as a dependent, you have no income in 2019 other than your one job, from which you will get a W-2, and your employer has withheld federal income tax from your pay. If any of these assumptions are not correct, post more details.
Based on those assumptions, if your gross pay for the year is $12,200 or less, when you file your tax return you will get a full refund of all the tax that was withheld. If you make more than $12,200 you will have to pay some tax. The tax that was withheld from your pay will be applied to the actual tax that you have to pay for the year. Since you only worked part of the year, the tax that was withheld is probably more than your actual tax for the year, in which case you will get a refund of the excess tax that was withheld.
After you get your first paycheck in 2020, you should use the Tax Withholding Estimator on the IRS web site to figure out what to put on your W-4 form for 2020, and give your employer a new W-4.
IRS Tax Withholding Estimator
Note that if you do not get a full refund of all the tax that was withheld for 2019, or if you expect to make more than about $12,200 in 2020, you can no longer claim Exempt on your W-4.
