If you choose to use epoxy under your bolsters, make sure that it does not hardened in the pin hole. Otherwise, you will get the dreaded ring. You need to beat the snot out of the pins to have a chance at not seeing the ring. Try your best to not get epoxy into the holes and one the pins. It takes some practice.
Also, I agree with Bossdog. Use 3/32 pins. Not as large as 1/8 but way easier to beat and hide.
Also, make sure everything is clean, clean, clean. The holes, the pins, need a very thorough cleaning before attachment. Otherwise you can get the ring just from oxidation.
Also, make sure everything is flat, flat, flat. A good fit helps more than anything else in getting the pins to disappear. If it fits good pre-attachment, you will be able to pien the pins much easier than if you have a poor fit/alignment.
Also, at least for me, with 416 stainless steel, I try to have the bolster as close to finished and shaped before attachment. It is way harder than any other handle material and it is hard for me to not get a bump/divot/seam at the edge of the bolster material where it meets the handle material. Stainless is removed at a much slower rate than say wood, G10, bone, etc. I struggle with that particular area when using 416. Not so much with brass. It is a bit softer.
BTW: For a first attempt, you did fairly well. I can see where a little more pre-shaping on the bolster itself, before attachment, will help your end result. Keep trying and practicing. You will get better every time. But, that is a pretty darn good first attempt.
Instead of removing the bolsters, I would attempt to use a nail set and strike around the pins hole showing. Just go around each ring and try and beat them down a bit more. Obviously, you will need to finish them again if you attempt to fix the "ring".
Keep grinding.
Dennis