
White lilly- Can you start his recall quietly at home- Maybe put the other dogs in the garden for a while and just have him in one room with you.
Try using food or a toy (whichever one he loves best and just call him really hapilly. If he doesn't come don't go after him waggle the toy or treat moving backwards like a game and loads of praise, tugging with toy/ or treat when he comes.
He may have been told to "come here" when he has been naughty before and so have a negative association or only ever been called to be put back on the lead- meaning the fun ends when those words are said.
He needs to know that "come" is great and means yummies or tugs.
I used to recall my shepherds ten plus times on each walk calling them in for a quick touch/treat and then sending them off again.
I would wait until he is 100% coming back looking keen at home before trying outside.
He sounds full of energy and fun.
It's not great that you say you are a bit frightened of him- he will sense that.
How is his down stay? Maybe you can practice that so you feel you are teaching him whilst he is in a calmer position and you can gain confidence.
Gsd's are a bright breed and usually keen to please
Hope you sort things out