Should I change my w4 from claim 3 to 1 if I'm not married. Will it affect my return?

[Opus 17]

Are you using the new (current) W-4?  It's very different from the old form.

https://www.irs.gov/pub/irs-pdf/fw4.pdf

Claiming fewer dependents will mean you have more tax withheld, meaning a smaller weekly pay check and either a larger tax refund or less tax owed.

You should claim the correct number of dependents and allowances for your situation, whatever that is.  Read and follow the instructions on both pages of the form. 

[rjs]

The new W-4 form doesn't use allowances anymore, so you no longer "claim 3" or any other number of allowances. The new form works differently. Use the Tax Withholding Estimator on the IRS web site to figure out what to put on your W-4 form. It will show you how to adjust your withholding to get the approximate refund amount that you want.