My PC stays at 100% usage while gaming. The temperatures are low (max 78 C).
My Specs:
Intel Core i3 3240
Zebronics H61
GT 710
Hynix 4 GB DDr3, One Module
With all respect, and without being harsh or coming across as a jerk, an i3 isn't really a CPU for gaming. i3's are more common in office based builds, for word processing, internet browsing. Even some office computers use i5 CPUs.
Your system is relatively old, I don't know what games you are playing, but by the sound of it, it can't handle them and the games are being bottlenecked by your CPU, adding more RAM or adding another stick of it probably won't do much at all, so frankly isn't worth the cost.
I'd personally suggest looking to get a newer system, if you can of course.