What would cause a false-positive of ekg with new t-wave inversions in anterior leads?

Lot of Things. Lead: Placement commonly not done properly, electrolytes, meds, syndrome x & vasospasm. Problem with calling it "false-positive" is that there is no perfectly accurate gold standard. We are dealing with behavior, as recorded as voltage against time (that's what an ekg is), there are lots of variables & changes in waveforms can come & go for a large variety of reasons. Can't figure out long distance.

Improper placement: It would be important to clarify if it was truly a false positive. More testing would need to be done. If there is a thought it is a false positive then it would be important to repeat it first.

Ecg: In a 23y/o female you probably have persistent juvenile t wave inversion which can come and go. Other causes of anterior t wave inversion in a young person are less benign but the drugs you are taking can certainly also cause t wave changes. You should discuss with your doctor but not be anxious at this point about this.