You have to make sure your router base is centered. You use a centering cone for that purpose. Insert it into your collet and lay the base down on it. Raise the router (bit up), until the loose base is seated on both the cone and the router metal base. Lock the base down with the screws you removed to release the base. Now it's centered, and you will now have a centered bit. Put in a bushing on it and the bit is now centered in the bushing. This is a critical first step. Now you can use the formulas to compute the offset between the outside edge of the nipple of the bushing and the cutting edge of bit.
The circle template will need to be the same measure larger than 30 mm. so if the measure is 4mm, then your pattern needs to be 34 mm. That is if you are cutting a hole. If you are cutting plugs, you use the distance from the edge of the nipple to the cutter on the far side. If that is, say 16 mm, then your template would need to be 46 mm . If you haven't centered the bit, the results will be poor.
Or, if you are cutting an opening, use a drill press and a 30 mm forstner bit that has and edge cutter at the tips. Theoretically you could just use a drill for this, but it is really hard to get a really clean opening without a drill press. And back up the piece you're drilling with another board to avoid any tearout. Here's a 30 mm Forstner bit for $13.
https://www.amazon.com/Roman-Carbid...words=30mm+forstner+bit&qid=1657589604&sr=8-5
Here's a picture of a forstner bit that has the tips to make a really clean edged opening:
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If I were cutting 30mm pucks, I'd probably use a band saw or jig saw with a thin blade, to cut out the first plug, then perfect the edge with sandpaper, After that you could use a small bottom bearing trim bit, tape the plug down, then use the router to cut the rest of the plugs.
If I were making a lot of these plugs, I'd find someone to turn a 30 mm rod and cut the pucks off using a stop block for length, and some sort of V shaped carrier to hold the round steady for the cutoff. Sandpaper the ends a bit and that would allow for as many plugs as I wanted. You might also be able to special order the 30 mm dowel from a mill that makes such things.
If there is a wobble in your router it may be that the bearings are worn, or worn unevenly, or there's something stuck in it. Get it serviced or replace it. A wobble makes a router the enemy of good work.
Lots of ways to skin this particular cat. FYI, here's a picture of a centering cone. You'll find them at Amazon or any woodworking store.