@Vyse Hey man! Welcome back!
The answer is going to seem pretty simple but yes, you just need to eat more. Remember that the numbers you get from any calculator, even here on this site, are just starting points to work from.
If you notice after 2 weeks or 3 weeks that you're not gaining weight, then you need to make changes based on your own results. Now it's possible that you were gaining muscle and losing fat, but if you feel like there's been no change in your physique for 3 months, then that doesn't sound like the case.
If you still aren't gaining weight at 2700 calories, try 3000 calories. It's great that you're gaining strength! But in order to build muscle you'll need to be in that calorie surplus and based on what you've said, it doesn't sound like you're in a surplus at the moment. It's true that you might be burning more than you think, so eat more to grow my bro!
Also make sure you are getting enough protein - protein is the building blocks of muscles!
Thanks man, hope you have a great weekend!