Summer Ale Low OG

I brewed my BB Summer Ale kit yesterday. Everything seemed to go well enough. I made a tea out of the orange and lemon peel and added it the last 15 min of the boil. Chilled the wort and added it to the carboy. I've been topping off to what I thought was the 5 gallon line on my 6.5 gallon carboy. I measured out with a 5 gallon wine jug and 5 gallons actually came about a good bit above the line. After topping off my wort I took an OG reading, somewhere around 1.037, should be 1.040-1.045. Too much water? Not steady enough of a boil? I suppose I've gotten hung up on volume and not checking OG before topping off with cool water. Oh well, lessons learned.

I pitched the WLP001 I harvested from my last batch of ale. I pitched it straight with no starter. The dude at the LHBS started it shouldn't be necessary to make a starter unless you're doing a higher gravity beer, which may be next weekends batch. At any rate, fermentation took off after about 20 hours and things are bubbling, albeit a tad slower and maybe slightly less aggressive than my last batch of amber ale with the same yeast. The low OG may account for that.

My last batch of ale had something of a low yield, 44 bottles, but OG and FG as I recall was within the range, so I guess that's what's important. I thought I had not added enough water, others have suggested it was due to possible evaporation. Maybe evaporation will be on my side this time so I don't end up with lemon flavored water.

Yep, common mistake, you added too much water. You should have topped off to reach the target gravity, not to reach a volume level.

Don't worry though, all you've done is lowered the ABV a bit. This is a light style, so you probably won't even change the taste, it is just going to take more of them to get drunky!

if this was an extract kit then you're at the expected OG if your volume was correct. it is difficult to properly mix wort and water well enough to get an accurate reading. I'd recommend taking a reading before topping off and just calculating the true OG:
batch OG = post-boil OG * post-boil volume / batch volume.