Thrift Savings Plan is a retirement plan, but you have to be more specific where you want to count the plan. You cannot deduct the contributions separately, they are already included on your W-2. You should have the box 13 checked, showing that you have a retirement plan, but you can't alter the form and just check it. If it is not checked, contact DFAS to correct it.
If you are referring to 1099-R distributions, the TSP is considered a Qualified plan.