First AG Batch, missed SG target

Well, first AG batch is in the fermenter, and I was looking for a SG of 1.060 or thereabouts after the boil, and I got 1.040. So if it finishes out at about 1.013 like I hope, it will be about 3.5% ABV. So instead of a Robust Porter, I'll call it my (Not So) Robust Porter. Meh, sessionable at least!

Lessons learned:
1-When you sparge for 20 minutes and you're already at 5 gallons of wort collected, you're probably sparging too quickly.

2-if you don't hit your target mash temp, call it a "step mash" and try again! lol i missed my target of 152 and decided to try letting it rest at 144 for 15 minutes, then added 1 quart of 192 water which brought me to 154, where I finished out. I'm not sure of the effect this will have, but I went with it!.

3-and not related to my actual brew process- screw glass carboys. i just shattered a 6.5 gal. one. No injury, no lost beer, just 6 gallons of star san/water all over the place and a bunch of glass chunks to clean up. now i just have to convince SWMBO to let me get a conical instead of buckets/better bottles... maybe if i don't tell her that buckets and better bottles exist???

Do you do an iodine test or check the gravity after the hour mash before sparging? If so what gravity do you aim for?
I know the wort is super concentrated before the sparge.
Maybe 1.080 or 1.1?

If this is your first all-grain then what you are experiencing is the beginning of figuring out the efficiency of your system. It's the old YRRMV. Next time add a little more malt or change your technique until you have a good handle on your efficiency and can estimate your recipes a little more accurately. You are headed in the right direction with your lessons learned. The important thing is to get more and more batches under your belt and after a while you will be able to do it in your sleep. Having something bubbling away in the fermenter that you made from scratch is an incredible feeling. Congratulations are in order!

I found a couple things that help increase eff.
1. Crush a bit finer and mash a bit thicker. In mash at 1.25 qt per lb. I also spray the grain with water before I grind. I helps prevent stuck mashes by squeezing the grain from the hull.
2. Definitely check your mash with an iodine test.
3. If you are batch sparging try to add bits of boiling water to get yourself up to 170(mashout temp). It will help you to rinse more of the sugar of the grain.
4. Don't be afraid to stir the he!! out of the grain and vorlauf until it's clear before pulling your running to the kettle.
5. Keep some light dme around in case your low and need some extra malt to hit your SG.

Then again I'm drunk right now

I think the OP hit the nail on the head with the sparge duration. All things being equal a slower fly sparge will be an improvement. As noted by others, keep track of the total grain weight and the in-the-carboy OG and volume. This will give you your brewhouse efficiency, allowing you to modify recipes to fit your system.

If you aren't hitting 90% efficiency, don't sweat it. 75% efficient beer tastes 100% awesome. So does 65%.