You don’t have to enter the TX transmit frequency if you’re using a GMRS radio and you have selected one of the repeater channels (which you have!) but you do have to make sure that you have entered the proper CTCSS tone or DCS code that the repeater requires or the repeater wil, just ignore any signal it receives from you.
No, kerchunking the repeater is not a very reliable way to confirm that you’re activating the repeater, especially if you’re relatively inexperienced. The best way is to push the PTT, say your call sign, and ask for a radio check.