It sounds like you're gonna be ok, you just got impatient. You're tank is still very young so it's still somewhat unstable and stability is what make a reef tank successful. A few suggestions...
If you want a second clown get one noticeably smaller than the one you currently have. You may also need to put it in a clear plastic box (I forget what these are called) for a while to let them get to know each other while still protecting the new one. I'd also recommend waiting at least a month or two to make sure you have everything else under control (water parameters, cleaning schedule). You'll have to make sure to stay on top of tank cleaning with 3 good sized fish (remember all of these fish will grow! Your watchman may be small now but that won't last).
You may want to switch from just carbon to something like chemipure and change it once a month. It includes both carbon and GFO (for phosphates).
Looking at your picture - take a good look at the green and red coral to the right. There might be a pest anemone right in front. You'll want to nip that in the bud ASAP (go to the hitchhiker thread and search for aptasia for ideas on how to ID and deal with it).
I like your scape. Nice arches.
By a clear plastic box do you mean like a breeding tank thing that has suction cups that stick to the glass so that they stay in the tank water, but are isolated from everyone else? I know I'm not actually using it for breeding, but I don't know what it's actually called either. But anyways, that's what we used for the firefish when he was sick.
And in regards to the pest on the closed brain coral (I think that's what it's called?), we used some "Aiptasia-X" and it hasn't worked yet, but it might be time to do it against. So we also got a peppermint shrimp which is supposed to eat it, but we've had him a week and he hasn't made it over there yet...
Thank you so much! Looking at all of the pictures on here makes me think we need more LR! But I loooove our middle rock because it has so many little caves in it [emoji4]