It's a snap to calculate bicarbonate from alkalinity but it is alkalinity you are really interested in. If you are given a bicabonate number the first thing you do is convert it to alkalinity. The conversion is pretty accurate as long as pH (of the water) is below 8 or so but begins to fall off above that. That's why alkalinity is a better measure than bicarb. It is valid at any pH.
bicarb = 61*alkalinity/50.
Yes, 5.7 is high enough that you should do something about it. The beer will not be ruined by any means at 5.7 but will be noticeably better at 5.4 - 5.5. The correction is simple enough to do. Just add sauermalz (acidulated malt) at 2% by weight of the total grist. This is generally a better solution to pH adjustment than adding calcium for the reason you saw when you tried to do it that way. Another convenient way is to dilute the tap water with RO or DI water thus cutting the alkalinity. If you do that you will get a lower mash pH and require a smaller correction to the point where you may be able to get it with calcium additions.