Is it OK to send email to journal asking for extension for a revision?
Ask for an extension. This is quite common in case more extensive changes/analyses need to be done.

Submitting a subpar version would waste their and their reviewers’ time, and may even end in a desk rejection for you.

When asking for an extension, shortly explain why you need more time (ideally, related to the reviews you got – show them you are working on the paper), and make a good estimate on when you will be able to resubmit. You don’t want to ask for several extensions during the same round.