Boosting from mid 500s to upper 600s

Hi guys,

Long time lurker here. I love the vast amounts of information that is on here and I thought I'd ask for a bit of advice.

I wrote the GMAT in December and got an embarrassing 540. I don't remember exactly what the section scores were.
I am not upset about the score I received due to the fact that I probably studied for about 30 hours total over the course of 3 months.

I am planning on re-taking it and actually putting in effort this time. I am about to enter week 3 of studies and noticing it to be a true test of endurance and time management (working full-time, gym, girlfriend, etc.). However, I am finding myself successful in allocating 2hrs each weekday and 4hrs Saturday and 4hrs Sunday to study.

I took a GMATprep mock test before I began re-studying just to really see where I'm at and dissect my weaknesses. I scored a 530 Q34 V28.
I have always been a strong test taker as a student and was always able to pass exams with minimal to zero studying.
I know the GMAT is a different type of test which is why I'm here asking for help. I've noticed a lot of my errors (about 40%-50%) on the quant section were due to carelessness/not reading the question fully/reading too fast.

I understand that I will have to boost both my quant and verbal scores to get where I need to be.

Ideally, I would like to get into USC Marshall's MBA program and pursue a career in finance.

I was wondering if anyone could provide any guidance/tips/advice for me to reach my goal.

Materials:
OG 2018
Kaplan Math Workbook

I have looked into MGMAT's quant books as I've heard great things about them, but it is difficult for me financially.
I am open to possibly purchasing just the number properties book or something else that you guys would recommend that wouldn't hurt my wallet as bad as buying everything.

Thanks in advance