You'll definitely be fine.
One of my first all grain batches had a similarly disastrous mash. I was testing a new mash tun, one of those double bucket types where the inside bucket is drilled to create a false bottom.
Well I missed my mash temp, so I had to add additional water to adjust. All is good. Then 30 min into the mash, I notice that my mash lost over 7F. Dropping from 152 to 145. I add a bit more water, all is well and I'm back on track.
It's now time to collect my first runnings. Well nothings coming out of the valve. Turns out the holes I drilled are all clogged by the mash. I attempt to clear it by scraping the bottom with my metal spoon. I get the occasional drip into the kettle along with a few chunks of grain.
I then go to my equipment bin, pull out a large mesh bag, and place it in the kettle. I then proceed to dump the entire contents of the "mash tun" into it. I raise the temp by firing up the kettle and allow the grain to rest at 152 for an additional 30 mins.
Once my second mash is completed, I take a gravity reading and to my surprise, find that my efficiency is almost 80%!
The rest of the brew day went fine, and the beer, a California Common, turns out to be one of my best yet. As for the bucket mash tun, it went in the trash bin that night, and was replaced by an igloo cooler the next brew day.
So don't sweat it, you'll love this beer and you'll never be able to reproduce it.