The seat must be installed in the window position, so you will almost surely have to keep the armrest raised between you and the carseat, because the bulkhead armrest doesn't lift. (Armrests may remain raised in flight if they are firmly wedged in that position by a carseat or a larger person's back, carseats and "passengers of size" are pretty much the only exceptions to the rule that they need to be down for takeoff and landing.) It will fit, don't worry. However, you may have to argue about placing it rear-facing -- that will block all seat recline, and sometimes the FA's will take the other passengers' side, even though the law says that rear-facing is OK on a plane.