Very high OG, should I worry?

I just finished brewing a dark ale...i don't want to call it a porter because technically i don't know if it is. Anyway, the anticipated OG for this brew is 1.059, my reading came out to be 1.070. I checked the gravity just after pitching the yeast, is that the right time to check for the OG? Check out my recipe, see what you think is going on.
This is a partial mash recipe by the way.

Batch size: 5 gallons
Total extract: 6.88lbs
Anticipated OG: 1.059
Anticipated SRM: 18.6 Could somebody please tell me what this means?)
Anticipated IBU: 19.2
Plato: 14.5 (What does this mean?)

Wort Size: 3.5 gallons
Wort Boil time: 60 minutes

Grain/Extract Color-SRM Gravity

5lbs light dry malt extract 7 1.046
1lb wheat dry malt extract 7 1.044
.5lbs munch malt 8 1.037
.4lbs carafa 400 1.030


Hops Form Alpha IBU Boil time

1oz Hallertauer Mittelfruh Pellet 4.5 11.5 60 min
.5oz Tettnanger Tettnang Pellet 4.5 4.6 40 min
.5oz Tettnanger Tettnang Pellet 4.5 3.2 30 min
1 oz Spalt Select Pellet 3.0 0 10 min

Procedure
Bring 2 gallons of water to 160 degrees, steep grains for 30 minutes
Bring 1 gallon of water to 160 degrees for sparge
After sparge put the now 3 gallons of wort back onto heat and add malt extract
When extract is dissolved, bring wort to boil and begin adding hops.
After 60 minutes strain and transfer wort to primary fermenter which already has 2 gallons, or 16 lbs of ice, this is to act as a wort chiller.
When the wort reaches 80 degrees pitch yeast and check for gravity.
Let ferment 1 week at room temp. until gravity readings are consistent for a few days.
Rack to secondary for 3 days, dry hop.
When fermentation is completed, bottle and condition.

What do you guys think?

Did you add water to top up to 5 gallons and stir well?

SRM is the number given to the color to expect- the lower the number, the lighter colored the beer will be. The plato scale is like the balling scale, measuring brix. That is, measuring the amount of sugars in the liquid. I don't use it at all, so I don't know that much about it. I use the specific gravity measurement.

IT would have been 1.059 if you topped off to five gallons, with 3.5 gallons you got the higher OG

It's not possible to get 5 gallons at 1.070 with those grains and extracts (max would be 1.061, and that's if you got 100% out of your steeped grains. You either don't have 5 full gallons in your fermenter, or you didn't mix well and took a particularly dense sample.

You must have done some topping up b/c it's also not possible to get 3.5 gal at 1.070 (would have to be higher than that, based on the extracts alone) but it sounds like you came up short.

Thanks you to those who have replied so far. Everything that i've read from you all makes a lot of sense. I don't know if I have a full 5 gallons in the fermenter right now, I'll have to check when I get home.
Another thing I thought of is maybe my hydrometer isn't calibrated or something like that...either that or the sample i took was a bit too dense.

Thanks again!

Mix well and top up to 5 gallons....

High OG is nothing to really worry about, just means a stronger beer. If you really want to get it to your anticipated OG then top it off with water till you get that OG and you might have more than 5 gallons, but like every one else said, you have 3.5 gallons posted as your volume, if you dilute it to 5 you should get your target.

The Plato scale is very nice for working with the specific gravity. 1 degree Plato means 1% of the weight of the liquid is sugar. It's almost exactly proportional to the last 2-3 numbers of the specific gravity scale, divided by 4. So your anticipated OG it says 1.059; divide 59 by 4 is just a hair under 15. That recipe is more specific on the OG value than the Plato value.