File the partnership return ASAP and issue the K-1 forms to the partners so they can file their personal returns.
WHEN the IRS sends you a bill for the late filing you can beg stupidity (since this is your first time filing a 1065) to get the penalty abated if you promise to never do it again. There is only ONE abatement allowed per business. Next time simply file an extension form 7004 by 3/15 to get until 9/15 to file the return.
