First: 100mA Voltage ... Ampere is the unit for current, not for Voltage, so that kind of doesn't make sense.
Second: A schematic/circuit diagram will make it a lot easier to help you. Please include one.
It's easy to adjust the gain of an op amp with the change/additon of 2 resitors, but without a circuit diagram it's hard to tell what you're trying to achieve or what your circuit actually looks like. And that makes it not easy to recommend anything.
Cheers,
Florian