Goop also forms bubbles when you move it. Try to put it on in one smooth movement and then don't touch it until it cures.
I had one that bubbled like that, but I was still able to get good bottom returns at more than 600' I don't think the bubbles matter that much unless the Goop layer is really thick. I always press the transducer down so there is very little Goop under it. I put a thick layer of Goop up the sides and over the top edge to get a good hold on the transducer.
I'm not convinced that all the bubbles came from the curing. With such a thin layer of Goop, it is possible that some of this happened when they were pried up.