Hello!
No need to get discouraged. Hard work can improve things significantly. This score you got on that practice test is only your starting point. There're a lot of retired GMAT problems to practice. If you analyzed most of them carefully, and your score didn't improve, only then maybe it would be time to start worrying.
You said that you didn't finish on time. In fact, this is what you have to avoid on the real test. Not completing the test affects your score more than if you answer the questions incorrectly. So, if you see that only one minute is left, guess.
https://www.manhattangmat.com/blog/index ... nt-part-1/
It might be very useful for you to read this article about time management on the GMAT. The most important thing from the article, I think, is that if you have to guess on some questions, it's better to start guessing in the middle of the test (so as not to get a string of wrong answers in a row - it damages your score a lot).
To improve your reading skills (speed of reading, in particular), you should read a lot in English.
