Need to get ABV higher...need some help

Doing a 20 minute boil on a Mexican Cervesa Beer from Midwest Supplies as a birthday present to someone.

O.G. was 1.036 (Instructions said it should be between 1.044-1.048)
F.G. at this time is 1.010 (Instruction said it should be between (1.010-1.014)

Looks like ABV should be around 3.7% when all is said and done. I would like to get ABV to 4.3-4.5%. Don't know what I did wrong when I took O.G., but it came out lower then expected. I know temp. at time O.G. is taken could have been an issue in regards to an incorrect O.G. reading, however, I was irresponsible and just took O.G. when wert was cool to the touch rather then taking an exact temp.

Any advice on how I could do this without ruining integrity of the beer would be great.

Thanks

Mix the top up water with the wort better/more vigurously and take another reading. I bet it was a case of the heavier wort sitting at the bottom while the light top up water stayed on top were you got your reading from!

andoniu83 said:

Doing a 20 minute boil on a Mexican Cervesa Beer from Midwest Supplies as a birthday present to someone.

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Is this an extract kit? If so, you hit the proper OG unless your volume was off.

I had a similar problem with a honey blonde ale i made!! it was a partial mash that i created, but i found that i didn't soak the grains long enough so i didn't get a full starch conversion. my O.G. was 1.035 when it should have of been 1.050 according to beersmith. After the first week it was down to 1.005 so i added a pound of corn sugar(boiled with 3 cups of water) and it brought it back up to 1.015 and i checked it after 3 days and it was back down to 1.005, so my guess is that i got another 1% which brings it to about 4.9%abv. Flavor wise, it made it a bit drier in taste, but i said screw it and decided to dry hop it for awhile to just try it out! Good luck with your brew!