Last year when I did physics only 2 people at my school got an A+ for physics (me and another guy).
With physics the unit 4 exam may be about the same in difficulty but take my work: "Do not think because you got an A+ for unit 3 you'll get one for unit 4". I probably didn't put in as much study for the unit 4 exam and finished with a stinking A.
With that decision my plan to get a 40 in one of my subjects was ruined.

Its all cool.
With most subjects if you get say 2 B+'s you can expect 33 - 34 (maybe 35), 2 A's 35 - 38 (maybe 39) and A+ 39 - 50.
Bottom line if you are beating yourself up about getting an A, don't its still a great score to get for an exam.
But juggling all your subjects apart from one or two will be much more of a challenge than this.