The charts in SnG strategy are only a starting point. I am working on push/fold charts of my own, making them with SnGwizzard (only just starting) but the charts are real game dependent - turbo, 6 max, 9 man, 18 man etc - and also must be flexible according to position, which is not real detailed in SnG strategy. And are table dynamic dependent, if you are not multitabling, meaning if you have reads, the charts are a basis for your decision, but take your reads and table dynamics into consideration too.
And ditto the comments on variance. You can lose many hands after a correct decision. Dont let that make you change a correct strategy. Review your game, and if you are playing correct, live with the variance. It will turn around soon enough.