Wire issue after changing battery cable

So recently I changed my cars positive battery cable to a new PICO brand 4g battery cable and now my car seems to have problems with power on the first turn of the key. The connector for the fuse box on the battery is where I am guessing the problem is because the connector wasn't exactly designed to fit the new PICO terminal so I made it fit as best as I can and tried to make the connection as solid as I can, but it still has the issue. On the first turn of the key after a while of the car sitting around the car starts extremely rough and then shuts off, and on the second turn of the key it starts with no issue, but if it sits for only a few hours then it will happen again. Something similar happened before I changed the battery cable but on a much much smaller scale. Before the car would take a few seconds and sometimes randomly honk upon when turning the key, and would start slightly rough but even out after a few seconds.