You need also to consider the execution. Demo execution is what you see is what you get, but not on live trading. You will get so called slippage / price adjustment - depending of the order sizes. In most cases this would be negative for you, which means worst entry and exit prices. In some case you will have positive slippage, but not in the same size as negative.
Another point is entries or exits in gaps. They will be different on demo and live and this will have influence also over the final result.
Bottom line: the gaps most likely will be not so often and with such sizes that could affect strongly your strategy, but we have some events as : Brexit, France elections, Turkish referendum and etc. that needs to be considered. :)