I wouldn’t freak out quite yet, it’s definitely better to be proactive and avoid having these pest in the first place (dipping corals before adding is definitely a good place to start) but it’s not the end of the world (at least not yet hahah). Idk if the rock they are on is small enough to be pulled out but if it is I would quickly take it out and scrape the aiptasia off. Did you buy live rock? If so it probably has other aiptasia on it, people have used products to get rid of them like aiptasia X and have even squirted lemon juice at them in order to kill them; others have added peppermint shrimp or berghia nudibranchs so that they could eat the aiptasia.