I mean, you don't really need a settings menu or any of that stuff. Most of the attention is on the timer (having the timer be a fraction was clever, I liked that), the equation, and the submitting of answers, so it makes sense in a way, especially with a timer on hand.
If I were to critic the art, the background art is nice, the fog effect/ gradient is really nice and soothing to look at, especially with the chosen color palette; and the smooth clouds are a nice change from the typical bubbly ones I see most of the time. For the text, such as the title and equations, it is a little hard to read at first, so it may be a good addition to change the color or have an outline or something behind the text to make it pop out more. The simplest and cheapest way to do that is to just duplicate the text box and move it a few pixels over and change one of the box's text color. (very effective and is something I did in my game for example).
It isn't a terrible thing to have people comment on things you never expected, but more people should complement on your positives instead of repeatedly commenting on the same flaw. And again, for 3-4 hours of work, you did a great job! People still loved playing what you made, and that's always the best possible outcome.
Till next time, cheers!