You should keep as much documentation as possible to support the gambling winnings and losses you report on your tax return, in case of an audit. So, you should get a transcript from the casinos if possible. The spreadsheet by itself may not be sufficient as you need documentary evidence of the amounts you enter on it.
As mentioned by @Cynthiad66 , you can only enter your losses as itemized deductions. So, you shouldn't enter them as a direct adjustment to income.
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