Hi
There is more chance of this happening if the trigger block repeats, but it is very difficult to say for sure without seeing how your trigger is constructed.
I would suggest to check the frequency of the update of the list of bets in the settings is appropriate for your market refresh rate etc. The default setting of 3 secs should be fine for football markets.
Then try adding a couple of conditions to the betting trigger to make sure there are no bets already in the market:
if you are backing:
and markets number of unmatched back bets is equal to 0
and markets number of matched back bets is equal to 0
if you are laying:
and markets number of unmatched lay bets is equal to 0
and markets number of matched lay bets is equal to 0