Well, I'm not really a fan of ADC's, but I think I can spot your problems right off the bat. Building BotRK as your first full item will contribute significantly less damage than almost any other ADC option. Keep in mind, BotRK is an item designed to help kill tanks, which is why it sacrifices raw AD for the % health damage. Against most champions in the botlane, this is a very poor tradeoff, and you should be focusing more on building damage that will be effective against squishier targets (like the opposing ADC).
Second, you shouldn't be building Guinsoo's Rageblade for any reason as Kalista. Half of the item gives you AP, which Kalista doesn't scale with at all. That means you waste a ton of money to get an item that does very little for you. Again, you want to invest into more traditional stats for an ADC, such as raw AD or perhaps attack speed and critical chance, as this will dramatically increase your overall damage.
Finally, if you are grabbing any item with critical chance, such as randuins, you really want to max out your critical chance. It tends to be something of an all or nothing stat, otherwise it is a lot less valuable.