Layoff date is not important. It's the number of months that you were covered by a HDHP that matters.
"the HDHP was paid for through 10/31/16 by my former company and I paid myself for a different health plan for November and December."
If you were covered by a HSA for all of 2016, you can contribute the full $3350.
If the "different health plan" for November and December was not a HDHP, then you are only permitted 10/12 of $3350 ($2791.67). You must withdraw $558.33 to avoid a penalty for excess contribution. The withdrawal must be an "excess contribution withdrawal". Contact your HSA administrator to request the withdrawal.
