It depends on the total pot, and I'm sure no one will have 100% chance of winning unless you are the only one who play. Lets say you send 1btc and the total pot is 2btc, means that you have 50% winning chance.
Someone with 1% still have the chance to win the prize because it is provably fair lottery but he will need a great luck to win with only 1% chance.
This is correct, thanks for the explanation.
Each time someone plays, the value of the pot increases, and thus, all the probabilities are recalculated accordingly.
Each satoshis played gives you one chance out of the number of satoshis in the jackpot to win.