The main verb in a subordinate clause that starts with как бы не has a perfective aspect. And as with бы(by), the main verb takes the past tense form when it is finite.
If the main clause and the subordinate clause that starts with как бы не have the same subject, then the subordinate clause can have its main verb as an infinitive without a subject (as the missing subject is already implied in the subject of the main clause). For example:
Моя коллега беспокоилась, как бы она не встретила своего менеджера. (My colleague was worried that she would run into her manager.)
Моя коллега беспокоилась, как бы не встретить своего менеджера. (My colleague was worried about running into her manager.)
The main clause can be implied by omitting it, especially when it is used in a colloquial setting. For example:
Я боюсь, как бы не пошёл дождь. (I'm worried that it's going to rain.)
Как бы не пошёл дождь. ((I'm worried) that it's going to rain.)