Onepapel website is not working for me, so only thing I could check out is your github page.
We already have one bitcointalk community project that is provably fair, and made by our member bitmover.
Name of this project is Bitcointalk Giveaway Manager, it is free to use, and it is all based on bitcoin blocks.
Many people use this for selecting giveaway winners, and you can check it out and compare it with your service:
https://bitcoindata.science/giveaway-manager/