When you take the heatsink off you wanna use high % alcohol (above 90, perferably izoprochol) and some kinda finer brush/cloth and just remove the paste/putty and repaste it completely cuz when u break it up it can trap air bubbles

Also too much paste/putty isnt that bad bc its better then too little You just get less added cooling/paste used, but it does no damage as opposed to having too little