Can I use drag and drop system, using templates, for a client on Squarespace?

So, I am not a web designer but I've created 2 websites using Weebly once before and Wordpress. Recently, I've gotten a client wanting me to build a website for her catering company. I want to do this for her because I need the money and I know how to use the drag and drop system. It's easy and fun to me. I was wondering If there would be any problem doing so and If I would need to contract this out? I also needed to know if I should become a REAL web designer first before I do service like this?