Title says it. I submitted a transcript in my online application for grad school but did not include the back side which contains the transcript legend (has some general info about my university and grading system). Should I worry? Would this affect my application? And should I send them the legend now?
Unless your undergraduate university has an uncommon or very different grading system than that of your prospective graduate university, this should not be a big deal. Your prospective graduate university will most likely ask you for originals or certified copies of your documents when you are admitted.
The uploaded documents have no official value and are used by the committee to decide on your aptitude for the program. As long as no important information is missing, you should be fine.
That said, there is nothing against sending them the full document now, so go ahead if you are worried. The worst that can happen is that they ignore your email.