The particle しき greatly resembles だけ, but it is no longer used a lot and is very limited in usage.
しき is seen after これ, それ, and あれ to express that something is "only about...much". The particle しき derives from 式 meaning "style". しき is synonymous to the pattern たかが…くらい.
It's just this much.
Don't whine about such an insignificant problem.
Don't worry cause it's only just that much.
You mustn't be astonished at such a mere thing as that.
Orthography Note: You may write しき in 当て字 as 式.