I disagree with others and do not think you need to take additional courses and spend more money than you need. But if you don't register for at least another 6 credits, then you should be doing another 15-20 hours of volunteering/clinical work/paid employment to make up for the extra free time in your schedule. You can show that you have excellent time management skills without spending thousands of more dollars on coursework that you don't need.
Having said that, if there is an elective you are passionate about and have always wanted to take, it would show academic curiosity to go above and beyond what you need to take and show that you have academic interests that compel you to take courses of your own volition. However, that's assuming anyone noticed that you only needed 7 credits to graduate. And I am almost certain that no one reading your application would take the time to figure that out.
So really it's up to you. Your original post indicated that you were perhaps concerned with the cost of your education. In that case, think about how much better financially it is to work for 15-20 hours instead of taking another 6+ credits "just cuz". Instead of accumulating debt, you would be gainfully employed and could even make payments on the debt you already have. As long as you are using fruitfully those extra 15-20 hours per week that you save by not taking the additional courses, adcomms won't judge you negatively for taking 7 credits in your last semester.
If you hadn't already done 7 other semesters of full-time work, the answer might be different. For someone doing a post-bacc, for example, if their undergrad GPA were something like a 2.9, then taking 6 credits a semester and getting A's still wouldn't send the message that they can handle the work. But you have already taken tons of semesters of full-time courses and ostensibly done well, so much so that you only need 7 credits in your last semester. As long as you use that free time effectively, you're fine.