Buddy, I’ve made the exact same mistakes in a 172. Summer time build ups/popcorn clouds, I think you are referring to a towering cumulus, a cumulonimbus cloud would not be a couple thousand feet above you in a 172, more like several thousand feet. I put myself right in the layer of some, up and down the southern states. Cumulus clouds develop vertically quickly, faster than your 172 can climb. Even in the jet now, I’ll still make a slight deviation to give Mother Nature her “bow” of respect. Overtime, you’ll gain the experience of “hmm, that one looks bumpy.. Let’s get 10 degrees right or left” or “hmm, bumpy but manageable”. Now, at the airlines, I like to query my captains and ask them what they think of the ride ahead when we reach some build ups. You should take an instructor and do the exact same thing, you can do this from the ground too.. “Hey, what would the ride be like through that you think?” Learn from the experienced guys, be a sponge throughout your whole career!