Help, Training Advice Needed??

I've been training towards a 60 mile sportive at the end of March. Everything was going well until a few family commitments all came along at teh same time. Then my 1 year old son started teething badly.

So I've lost a couple of weeks training before the event. I'm worried now that I'm not going to have the necessary condition to do the ride, the most I've done before is 50 miles.

I was thinking a couple of weeks of HIIT sessions might help or should I just keep to my normal routine??