Your Rhododendron is growing happily. Look at where this year’s flowers were. ..... on the tips of the previous year’s growth. So don’t chop off the new stems. Unless, of course, you don’t want any flowers next spring.

What variety is it? Will it have sufficient space in that narrow bed?

I don't know what variety it is. When it gets to a certain height, can I prune to maintain the height I want?

This is the tag on the rhododendrons

English Roseum is a large growing variety that will get to 6-8 feet tall and as wide. If you need to prune to maintain a specific smaller size, you will seriously reduce its ability to flower.

It is not going to fit where it is. It needs to be relocated where it will have the ability to achieve its intended size without interference.

Rhododendrons require no pruning other than to remove any dead limbs or to rejuvenate old, neglected shrubs.

Would it make sense to get a rhododendron variety that grows 3' to 4' in height? I know that they have these varieties.

If you want a rhododendron for that particular spot, then yes, you do need find a smaller growing or dwarf form. Of which there are many, although since your location is unknown, they may not all be suitable for your use.

I am located on Brooklyn NY. Which smaller varieties of rhododendrons  would work for my zone and use?

Gosh, almost too many to list.........PJM Compact, Blue Diamond, Cream Crest, Aglo, Everred, most of the yakushimanum hybrids. It's pretty much just a question of color.

Find a nursery in the vicinity that carries a wide range of rhodies and ask to see what they have to fit your size requirements.

You should be in USDA hardiness zone 7b so you are not much limited by your location. Most rhodies will thrive in that zone, provided they receive the right growing conditions.