If the gains attributable to the $200 were $27.66, not $727.66, that makes a lot more sense but still represents about a 17% gain between March 28 and April 7, which is still high if your entire investment is in the S&P 500 fund.
Regarding the amount in box 2a of the Form 1099-R, I don't know if the custodian will aggregate the loss on the $100 returned contribution and gain the $200 returned contribution or if they will only show just the gain. I think they should aggregate the two, but that doesn't mean that they will do that.
