The $7 is the one time gate fee. Once you get your camping mirror tag you can come and go as you please for the length of your stay, 1 day or 14 days you only pay it once. If you were near other Indiana State Parks or Recreation areas, your one time $7 gate fee would have gotten you into those parks as well with your mirror hang tag dated with your departure date. If you change parks that you are camping in, you would pay the $7 gate fee again once at the next park.
Indiana residents can buy an annual pass for $40 and out of state guests can buy an annual pass @ $60. This will get you into all state properties as many time as you want and you will then only be charged the camping fee.