Newb SG concern

Hello all.
I did my first kit recipe about 10 days ago. I followed the boil directions precisely. I then ice bathed the wort and blended with my measured top-off water in a 6.5-G glass carboy, and aerated for approximately 5 minutes by rocking the carboy. The measured liquid volume in the carboy was near exactly 5-G. (Instead of the dry yeast that came with the Caribou Slobber kit, I purchased a White Labs English Ale WLP002 from my local supplier.) My OG was 1.015.
I was surprised and concerned, so I turned to the Internet where I determined that I either measured incorrectly (I measured several times due to my initial concern) or I didn’t blend the wort and water well enough, so was getting a bad sample using the thief.
The second day, the fermentation was extremely active. Quite a lot of off-gassing and activity in the carboy. So much so that the foam and solids were accumulating in the air lock that I kept filled with a Star San solution. However, it never plugged the air-way and gas continued to escape.
Activity slowed substantially by maybe the 4th or 5th day. On the 8th day I took another SG sample using my sanitized thief. To my surprise, the sample once again measured 1.015. So, of course, I am concerned again. I read the kits are pretty full-proof and that the problem is probably me. I’m wondering if, due to the length of the thief, and that it can only pull a sample from the top 3-4 inches of my brew, that would be giving inaccurate samples?
Any opinions,suggestions or words of encouragement will be appreciated.

You can be assured with NB kits that if you used all the fermentables in the kit and your volume in the fermentor is 5 gallons, the original gravity will be as stated in the recipe. It is very difficult to get the wort from the boil kettle and top off water mixed thoroughly for an accurate SG. I don’t bother with a OG reading anymore.

You’re thief seems to be more sized for one gallon batches. This is the one I use.

After fermentation begins the yeast will have the beer well mixed. SG will be the same from top to bottom. 1.015 is getting close to a possible Final Gravity. It may be too soon to be at FG though. Take another SG sample in a week. No need to risk infection opening the carboy for continuous SG samples. It will take about three weeks for the sediment to drop out anyway without cold crashing. Caribou Slobber has some complex flavors that need time to blend.

Getting the same SG reading is quite a coincidence. Could there be any sort of problem with the hydrometer? Fill your sample tube with distilled water at the calibration temperature for your hydrometer. The hydrometer should show a SG 1.000. the calibration temperature is printed on the card inside the hydrometer.

You’re lucky the airlock didn’t clog. It can cause quite a mess on the ceiling if the internal pressure blows it off. A blow off tube is good insurance at the beginning of a fermentation. Fermentations that are overly aggressive can be caused by the beer being to warm. Fermenting to warm can result in some off flavors. Yeast produces heat as it works. The temperature of the beer will always be higher than the ambient temperature. A swamp cooler is the most economical way to keep a fermentation from getting to warm.

I hope some of this helps.
Welcome to brewing and the NB forum.

Brewed CS three weeks ago had an OG of 1.047 and a FG of1.007. I think you got more water than wort don’t worry sounds like your going to have a very good beer when all is said and done.
Happy Brewing.