QFT. I spend a good bit of money on FB and my avg CTR isn't close to .08.
That being said, .08 CTR might suck for you ads, who knows on just 100 clicks. Short answer: lots of things can make it jump up and down. Rambling answer - below.
As for your actual question, why does your CTR jump around so much? You haven't established what your "normal" CTR is if you only have 100 clicks. Plus when you open up your budget, you open yourself up to more placements and new traffic.
There are a ton of variables that you must be overlooking if you are asking the question on a days worth of stats (and that small of an amount of clicks). Traffic quality changes from day to day - hell we have a trend with the offers we run there where I can tell you 3 different times of the day when our FB CTR will change as well as my conversion rates. If you have not run enough on FB to figure out when there are certain spikes and lows then keep running - and pay attention to your ads.
Another thing to consider is how big your target audience is esp since you bumped your budget up. Was the target small and you flooded the audience with a huge amount of impressions of the same ad? Were you running multiple ad copy (you should have been)?...
