My first recipe

Pay attention to how old your yeast is. I don't know the Brewtoad pitching calculator, but a good calculator will take account the age of the yeast. Older yeast means more dead cells which means you should pitch more.

 

What was the temperature of your wort (not the air temp) when your lid "exploded off?" And why do you think it's a fail....did you not clean and sanitize the lid and replace it (perhaps with a blowoff tube in place)?

 

You had "aggressive fermentation"...it happens sometimes with higher OG brews with lots of viable yeast. Next time you want to brew a DIPA or higher gravity brew, you may want to make and use a blow off tube/airlock to prevent the bung/airlock from exploding off. As VikeMan mentioned, as long as you resanitize and put the airlock back on, you most likely still have a batch that'll turn out just fine.

 

It's a good idea to monitor (and control) temperature throughout the fermentation. My guess is that your wort was very warm, causing a very fast/active fermentation.

Two smack packs in a high gravity 5 gallon batch was not too much. Not even close to too much. Not even if brand spanking new fresh.

 

Use brewing software/yeast calculator to figure out how much to pitch. Don't underpitch just because you had blowoff.

73F ambient plus heat from fermentation plus high gravity wort = big blowoff

Do a search on Blowoff Tube or Blowoff Hose.

 

Not trying to be an ass, but you need to read "How to Brew" by Palmer. Amazon sells a hard copy cheap or you can find the earlier edition online. If you have already read the book, you need to read it again.