Do deductions decrease my current refund amount?

Deductions can decrease your taxable income and therefore increase your refund or reduce your tax liability, but deductions cannot decrease your refund or increase your tax liability. If you're taking the standard deduction, which everyone gets unless they're able to qualify to use itemized deductions (not likely), then no deduction will have any impact on your taxable income or tax/refund that may be due. 

One caveat; using itemized deductions then some deductions can, depending on your income, trigger the Alternative Minimum Tax which then can impose an additional tax.