I want to learn Chinese and have a Chinese co-worker but she just laughs when I repeat the sounds she's making. She says I'm saying something entirely different because of the inflection.

I don't understand how you could since I've read the inflection of each word actually creates a different word depending on whether the tone is slanting up, slanting down, high, low, middle, etc. Can you yell at someone in Chinese or a tonal language like you can in English?
@ tone is not the same as volume

I raise my volume all the time, like when speaking to a group. I do not sound like I am angrily yelling them.