will eating back my exercise cals slowdown my weightloss ?

Yes it will. The more of a calorie deficit you create the more fat your body will be forced to burn for energy. Of course it is possible to eat so little that you stop losing weight but I doubt you are doing that. I'm a Physician Assistant in a weight loss clinic so feel free to message me with other questions.

Not eating back will create a bigger deficit, but everyone's body is different, I tend to plateau a lot. I would be stuck on the scale for 3-6 weeks and boom , One week I'll lose 7 lbs.
People told me I have too much exercise and not enough intake, but I average 700-1200 calories of burn per day on exercise, It's nut if I don't eat back some of the calories. Even then I'd plateau like crazy. To me it makes the transition to final maintaining that much easier. Once I reached my final goal, I can just do less exercise and still consume 1800-2000 calories a day. and maintain my weight for the long haul.
The cool thing is, I have push my goal weight back 3 times...Everytime I came close to getting it, I'd realize I have more to lose.

So, good luck!