Unfortunately, you can't cancel just one subject test score if you took more than one subject test on the same date. This rule applies regardless of when you signed up for each test. If you wanted to get rid of the literature test score, you would also need to cancel your math and physics scores.
If you're applying to colleges that don't require you to send all of your subject test scores, you can just send the math and physics scores and leave out the literature score. If you're not sure of the policies at the colleges where you plan on applying, here's a list of schools that require students to send all of their test scores. You'll notice that even many of these schools just ask for all scores from the SAT I and ACT and don't require you to report all subject test scores.
The worst case scenario is that you will need to send your literature score to one or more schools. In this situation, you can either retake the test at the beginning of your senior year (it's offered in October, November, and December) for a higher score or mention in the additional information section of your application that you mistakenly overloaded yourself with three tests on that day. Keep in mind that colleges don't care nearly as much about subject tests as they do about other aspects of your application. Also, you might end up with a better score than you expect.