if you owe money an extension does not delay your pay date. you will get fines or interest payments. OWED money is always due the 15th or earlier.

just an fyi.

get a cpa. google a local one. explain the situation. with a w2 generally the employer takes out taxes, so something is wrong with this picture. if you find someone whos sympathetic and the problem is an easy fix it could be under $500. assuming its straightforward and you dont have crypto and 10 brokerages and income from 8 jobs etc.

if its really straightforward (1 job, 1 investment account, nothing else) just use HRblock/walmart type of thing.