I imagine northern Oregon would have strong winds, fin repairs of the sort you are attempting are almost always doomed to failure, the stress on fins is enormous the break will reactivate under pressure.
Thrusters were designed to make turns easier but a 2+1 set up can give you a good turning framework.Buy a genuine set of fins from Futures the centre fin be any formate that fits the centre fin box, centre fin between 8 to 9 inches. Often there are reasonable cheap,secondhand centre fins
Cheap copies Chinese ebay fins are subject to,failure or have to be sanded to fit plugs or boxes.
Go basic at this stage in fins as improving your skills underlies everything.Practice turning from the back of your board, don‘t get stuck in one stance learn to move up and down the board, stepping back to weight and drive a turn , not just lean turn.
Experiment have fun , if you can elsewhere from rapid breaking shore break you may get time to do stuff in response to a wave

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