Archimedes -- pretty sure it was him, although I do get him confused with Aristotle -- says to measure a number to the degree needed for use. To the degree needed for use, the occurrance of a pre-specified sequence of 2**50 is impossible.
Obviously you skipped out of the lab assignment or you would (1) not be back yet, or (2) run the test on some massively powerful supercomputer and dimmed all of our lights to power it, or (3) been impossibly lucky. Of course, (3) is impossible.
You, yourself, agreed that any sequence has the same probability of occurrence thus "all heads" is no more improbable than any other sequence including the one that I tossed.
Are you claiming it is impossible to toss any sequence?