Locking the amounts doesn't change the fact that the tx info and the score is known before sending it to blockchain. Now I could try the different tokens, use different accounts, use other signers, shuffle the hivengine json or wait until refblocknum/refblockprefix match to reach the target score...

Check @magicdice - they solved this problem a couple of years ago. IIRC, they had a "secret" that was unknown at the time of sending a bet, but published a couple of minutes later. This way users could verify that the system was fair - but only for past games, not predicting current outcomes.

edit: found the original magicdice post with the technical details: @magicdice/magic-dice-tech-talk-provably-fair-and-transparent