Great giveaway but as willi9974 has already said, I would also determine a defined block after a sign-up deadline or until all numbers from 1-99 are picked.
By doing so, everyone could confirm who has won because Bitcoin's Blockchain is public.
Like
here.
However, it's up to you as you are giving out the prize money.
My BTC-Address: bc1qtexnml3hdjs6evy7va95h2cf3k5kkmhrdw4z6s