GMAT Online was a disaster - need help now for one week power prep!

Hello guys,

First some background:

My Goal was a score of 600+ and I started preparing full-time for the GMAT in November 2020 with the OG Book. After a week of getting familiar with the concepts, I did a mock test, which was 570 (Q41 V28). From then on I prepared myself with questions from the OG Online Question bank (Wiley), wrote a summary for theory and solving most quant problems, watched some youtube videos on strategies and focused on the areas which where not working that good. End of December 2020 I took another mock test and it was 660 (Q46 V34). Therefore I thought i was ready and took the GMAT Online Test beginning of January. The Quant section was really bad and i remember guessing a lot and i was not able to finish because i was running out of time. For the verbal section I had a good feeling.
After a week the results came: 370 (Q6 and V33) !!! I was devastated and thought what happend there, i mean that shows i got basically every single question on quant wrong!!
Afterwards I took a break from studying for about a month until now, because I had to do a lot of other things.

Now i decided to give it another try to score above 600, but the latest available date for the GMAT Online in February is the 17th (I cannot take a date in march because of the application deadline of the University). I was thinking that I most likely got a horrible day on last test day and that this does not show adequately my quant skills, which i think should be sufficient according to the mock test.
I wanted to do one full week of power prepping the quant section and then hopefully be able to score above 600. For the verbal section i will only practise a bit, because 33 should be sufficient to reach 600 when i am able to reach atleast 39 in quant.

My question is: What do you think I did wrong last time and what advice can you give me for this week?
I was planning to continue doing easy+med quant questions from the OG Online Question Bank until I am faster at them (i can solve most of them but it takes me sometimes a lot more than 2 minutes) and solve more of them right.

Are there any must-watch videos which could boost my score or show me new efficient strategies? I am aware that this is not a lot of time and ofc not enough time to rewatch every quant chapter in detail, I just want to reach safely the quant level i reached in the mock tests...

I sometimes saw that paid courses are advertising with unique strategies, are they worth it for my level or more suited for people scoring 700+ ?

I am open to all tipps in general regarding my goal.

I hope you can help me a bit, thank you already a lot!