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Unless you are a professional gambler, gambling losses are only deductible as an itemized deduction on Schedule A and only up to the amount of gambling wins. See https://www.irs.gov/taxtopics/tc419 for a discussion on that topic. So you don't directly "offset your losses." (If you are a professional gambler, I would assume you already know what you are doing and have a competent tax advisor.)
Assuming you are a regular cash basis taxpayer, you would report only the actual cash/check/prize monies received for your bets. Unless you could withdraw the deposit match or the free bet allowance without gambling, that is not income. Think of it as either a discount in the price of playing or an adjustment to the payoff of a winning bet.
Bottom line: Just report the total winnings, typically as W2-G gambling income, and use the actual money you laid down for gambling as your outlay for Schedule A deductions, capped at whatever your total winnings were.
Most people find that their standard deduction exceeds their itemized deductions these days and often by quite a lot. So it is quite possible, even likely, that the gambling loss deduction on Schedule A will give you no tax benefit. However, you alone know your actual situation and level of gambling activity. In any event TurboTax will calculated your itemized deduction total and compare it to your standard deduction to give you the one that minimizes your taxes. See Schedule A Instructions for a complete list of itemized deductions you can include alongside gambling losses.
