300 calories Eating... weight gain/lose weight???

I eat roughly 300 calories a day (I've been doing this for 1 month), I dont exercise and I have lost around 8kg(17.6lbs) so my question is, If I boost it up and eat say 800 calories a day wll I put all the weight on that I have lost??

-Proffessionals or people who know alot about this stuff, answer only please
Please dont say nasty things cause I am feeling bad about this already