Really? 11 of the 12 stories got rated higher when spoiled, which is decent evidence against the nil hypothesis (spoilers have zero effect on hedonic ratings) regardless of the error bars' size. Under the nil hypothesis, each story has a 50/50 chance of being rated higher when spoiled, giving a probability of (¹²C₁₁ × 0.5¹¹ × 0.5¹) + (¹²C₁₂ × 0.5¹² × 0.5⁰) = 0.0032 that ≥11 stories get a higher rating when spoiled. So the nil hypothesis gets rejected with a p-value of 0.0063 (the probability's doubled to make the test two-tailed), and presumably the results are still stronger evidence against a spoilers-are-bad hypothesis.

This, of course, doesn't account for unseen confounders, inter-individual variation in hedonic spoiler effects, publication bias, or the sample (79% female and taken from "the psychology subject pool at the University of California, San Diego") being unrepresentative of people in general. So you're still not necessarily a total freak!