Need some serious help/advice

Hi GMAT experts,
I am taking my gmat in 16 days. I need to score in the 600's. I have been consistently studying for a 1.5 months now. Diagnostic test score before any prep was 470 (V31, Q25). Took another practice test after about 3 weeks and scored 450 (ran out of time on both secs) . I was so bummed. Most recent practice test score was 540 (Q32, V 35). I recently started following the Magoosh 1- month study plan. Is there any hope that I might be able to score in the 600's on the real exam if I devote 10h/day? I tend to get extremely nervous on the practice test (even though I know its not real). If I am doing just a practice set of questions (e.g a set of 35 quant question (timed)) I tend to get 60 correct but on the practice it drops drastically. Moreover for the verbal section, in the OG I have gotten almost all SC questions correct every time! and for CR maybe about 80%. But it doesnt reflect on the practice exam. I feel like my mind just closes up and I cant think straight! Moreover, I have this feeling the whole time that I am getting every question wrong and I just want it to be over. For example, when I did the practice test today I thought I had gotten each of the first 3 quant questions wrong. In fact I had these all correct but I almost gave up halfway. Sorry for the long post but please provide some guidance. Rescheduling the test is currently not an option. My backup plan is to take the GRE if I dont do well on the gmat.

Thanks,
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