I just built a home hockey rink. The water finds it's way around the outside of my boards and tarp. Any help? Answered

I used 2 x 12 boards and wrapped my tarp/liner on the outside. But I only wrapped it 2-3 inches.   I thought wrapping the liner on the outside would be best so it didn't get beat up by my little hockey players.  But in the end, it appears I needed to wrap it all the way up on the boards.  It leaks up on the low side and drains. I thought it would the water would freeze up against the board and form a "seal".   But it does not.  It appears to be a major problem.  I am thinking of taping another strip of plastic along each side, using snow/ice duct tape.  But I'm worried about it not sealing. 

Any ideas on how to fix my problem would be greatly appreciated.  I don't want to/can't start over. 

Thanks!