There are always times in life where things turn to the unexpected. People miss career opporunities by unfortunate turns of events, whereas some make random moves without much deliberation - but in the end success is not always determined the very first day you move.
From what I understand, you love coding, but it may also be the case (what I see) that right now it is critical to take an available job, given that it would be urgent to your situation. So, I think the choice can be this-vs-that in terms of responsibilities, as much as now-vs-too-late in terms of urgency of taking a job. This is indeed tough to judge, but as I said, whatever you choose, you're not stuck with that decision forever. It will takes several decisions over a long period to determine the direction in which your career ultimately travels.
Different professions have their own values and outlooks. In judging professions you should not do it as "this thing is better than that other thing." All paths have their own traits -pros and cons - and all need some talent and a lot of hard work to grow. While you are hesitant, you should ask - is it that you don't want to do this at all, or is it isn't a perfect fit and you'd rather do coding?
Here are some questions you should ask yourself and depending on the answers you may judge whether new position is suitable for you. They may also reveal the kinds of questions you can ask your potential employer:
Design might needs some creativity but different from ones you need for coding. Do you feel uncomfortable taking on the design assignment? If so, try to figure out exactly why.
Lets suppose, in the worst case, you may not get any coding at all. Do you see this as a dead-end to your career, or can it be a place that you work until a better suited opportunity comes along?
Do you really think design is all that bad - either lowly, or something you just can't stand?
Do you have any history of employment setbacks, or severe family responsibility that prevent you from taking up any risky assignments?
Do you generally feel very uncomfortable in experiencing change of work types or working environments?
As for you, and maybe many who might face similar dilema, for every "no" to these questions it seems there is little worry winding up in a bad place; for every strong "yes", you might consider waiting for more a appropriate position to come by.