> Is it a special pattern or is it explicable with the "usual" meaning of ?
It's meaning (2) in this definition. In this case, dake corresponds to an upper limit or the maximum possible. In English "only" usually implies a limitation or a lack but in Japanese "dake" can also imply exactitude, something like "precisely", or up to some limit or another.
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> I’ve _remembered_ everything I could, so now all I have to do is wait for the day of the test to come.
Not a good translation of , "remembered" should be "learned" or "memorised". Anyway here it means "I've learned to the limit of my capacity".
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> I followed the instruction and _did all that I could_ , but I have no confidence that I’ll have good results.
Yes, here again it is the upper limit.