How bad is my taxes going to be if I haven’t done them in three years

So much depends upon your individual situation.  The possibilities range from:

• You may have been paid by W-2 with reasonable Federal/state withholding, or
• You may have been paid by 1099-Misc, owe income tax and self-employment tax and made no estimated tax payments.

There can be penalties for not filing or late filing, underpayment penalties and interest.

If possible, obtain a wage and income transcript from the IRS so that you do not miss any income or possible deductions that the IRS would be told about.

Prepare the three tax returns so that you know the total scope of the problem, if it is a problem.

You may find that professional help is necessary.