First Brew!

So my first brew (BIAB) is sitting in my carboy bubbling away which means its time to reflect. First Brew https://ift.tt/2ZBtuLv didn't go as planned:-My target Og was 1.063 but I ended up at 1.054. I think this was because when mashing the temperature dropped from 149° to 140°. Should I have kept the kettle on my burner to keep the temp in range rather than wrapping it in a blanket?-The recipe says " 50-minute mash with 15 L of strike water; mash temp on target of 149 F. Mashed-out for 10 minutes with 8.5 L of boiling water to 168 F. Sparged with ~3.25 gallons of 168 F water for final volume of ~6.75 gallons." I did the 8.5 liter mashout, but didnt have an extra burner for the 3.25 gallon 168° sparge so I just added cold water. Can I disregard the water additions and just start with the full volume since Im doing BIAB?Recipe link: https://ift.tt/30TxSmj for the help! via /r/Homebrewing https://ift.tt/2LiNquF