I found an error in my exam that caused me to lose time on other questions, resulting in a lower grade. How can I appeal? I'm a student in college, and while I was taking a linear algebra  exam, I noticed that there was a mistake in the last exercise. Our exam is composed of two parts: multiple questions and  exercises. I usually prefer to start with the second part while everybody starts with the first one.
I spent about 15 to 20 minutes before I called the teacher and said that there is an error. He confirmed the error and announced it to the rest of the class. At the end, I left some questions in the first part blank because I ran out of time.
The problem is that I received my grade (16/20) and I'm not really happy because if I had more time I could've done so much better (19/20 if I had finished the  three other questions).
How could I ask him to upgrade my grade  and explain to him that I really deserve it and that I really need to have (19/20) so I can pass my semester?

Update:
I saw my teacher today, and he didn't even give me a chance to talk and said that there is nothing he can do. When I said that this is not fair and that I spent time to find the error he said &quot;You should've passed the exercise&quot;. I don't know what to do now, any idea?
How could I tell him to upgrade my grade and explain to him that I really deserve it and that I really need to have (19/20) so I can pass my semester?

Don't tell him how to fix the error, and don't open with this being a make-or-break for passing your semester. This will probably put him on the defensive, and make him less likely to be sympathetic. In fact, the first time I read your question, I thought you were in the wrong, but upon closer reading, I understood your issue better.
I was in a similar situation, except one whole quiz section learned about the error half way through, whereas the other two learned about it at the start of the test, through a TA's error. It was a headache for the professor. If I recall,  they ended up giving everyone in that section a percentage boost.
Be polite, and straightforward:

Hi Professor,
In our last exam, I pointed out an error in the last part of the test. I spent 15-20 minutes working on the question before I figured out the error. Since I like to start with that section, I wasn't able to finish the first part of the test. Because of this, I didn't score as well as I could have.
Other students didn't have to spend so much time working on this question because I found the error for the class. Is it possible to adjust my score to reflect this?

Honestly, he probably didn't even think of it, or forgot by the time he was grading. You have a totally reasonable request.