SoFi Technologies Inc (NASDAQ:SOFI) investors just swallowed a heavy dose of volatility vitamins. The fintech rocket ship announced a $1.5 billion underwritten public offering — around 4% dilution — sending shares tumbling over 7% in pre-market trading Friday, just a day after closing at $29.60.Track SOFI stock here.Normally, that kind of dilution sparks orderly chaos. But the timing has turned a selloff into a cliffhanger. The S&P 500's quarterly rebalancing gets announced Friday afternoon, and SoFi is sud ...