Is the decision to devote oneself to memorizing the Book of Allah by leaving studies that involve mixing appropriate?

Combining regular schooling with memorizing the Quran and studying the Sharia sciences is preferable. You have done well by avoiding mixed-gender schools. If it is possible to find another mosque for memorizing the Quran, or someone who can teach you in a way that does not conflict with your institute, that would be better for combining regular schooling with Quran memorization and seeking knowledge. If combining them is not possible, then the Sharia sciences are better.