if it hermied and knocked itself up, yes that'll be 100% female.
xx x xx can only result in xx.
each "x" or "y" is an allele. you make a little box of the cros xx x xy , for exmaple is 2 xx and 2 xy (draw a box, divide into 4, but x x along top of box and xy along side... how they criss-cross is possible outcomes of sexual reproduction. xx x xx is xx in all 4 boxes. The only way you get a male is if there was some contamination of male pollen.
so as long as no males were anywhere nearby, or you didn't carry it in on your clothes, should be female.
the bad things - a plant that hermies easily and pollinates itself is at risk of passing along a very detrimental trait. hermy from extreme stress or chemical manipulation is one thing, but if it happens naturally, that's due to genetics and that can be passed on. so, watch out for hermaphroditic plants. if you see a high rate of this, stop using those seeds. i wouldn't suggest using them in the first place, but each to their own on having fun.