Dan,
Cool to see you experimenting with making molds and parts. Like others suggested, for making FG parts using a FG mold would be ideal and it’s not that difficult, just takes a few more steps than silicone and resin. However now that you have created and silicone mold you could do a test and make a resin part. I really like Smooth-on products for silicone and resins. Their website offers a lot of helpful videos but i’m Fortunate to live close to them so i can get help in person. Anyways, if you’re interested try some smooth cast 65D and use your mold and roto mold the new part. Mix the resin. Pour some in half the mold, clamp both halves together and manually rotate the mold in your hands 360 degrees round and round (basically a poor man’s roto molder) while the resin kicks off. 5-8 mins then let cure for another 5-10 mins before opening the mold. You will wind up with a complete resin part. To get a thicker wall just use a bit more resin, some experimentation may be in order, but once you get the amount to your liking you could knock out 3-4 parts in an afternoon and have some spares. Also you can tint the resin if you want (not sure what color you need your final part) but that also saves you some finishing time.
Just a thought. The fact you don’t have a clean part line isn’t a problem, in fact it helps the two halves key together better. I often use their sorta clear series of silicone to make molds and pour it around my part completely in a block then (because it’s clear) cut the mold apart to remove the plug.
Hope this wasn’t too wordy, happy to share any suggestions on this topic if you want.