There's nothing you can do about it, this is the issue you face when you have such an unusually individual study plan. People with REGULAR degree structures also encounter these timetabling issues. Also, chemistry tutorials do not take a roll even at second year (to my knowledge), and I'm sure if you talked to a tutor they'd be willing to accomodate you in their tutorial. You really have no more grounds for complaining than any of us do with our own timetables; lots of other people here have late class times. Everyone has to deal with minor inconveniences at some point, and the uni can't prevent all of them from happening, though I will concur that the Science Student Centre has its fair share of not-particularly-knowledgeable staff.
tl;dr it sucks, but lots of other people are in the same boat and you/the uni can't really do anything about it (and again, chemistry tutorials don't take attendance)
P.S. consider yourself lucky that the subject you're in has more than one or two tutorial times to choose from; there are subjects with single sets of classes and no alternative practical or tutorial times, where clashes or annoying breaks are completely unavoidable.