Yes, after sewing your strips together you should have a 4.5" wide strip set. And your new 1/4" foot could indeed be the culprit. My machine has a 'scant' 1/4" setting which is what I use. Long ago I had purchased a 1/4" foot w/guide and my seams were waaaay off! I also find that most of today's patterns - even if not specified - are referring to that elusive 'scant' 1/4" seam - which is a thread or 3 short of a 'true' 1/4" measurement.
And, yes, if your blocks are set 'on point' - i.e., the points are top/bottom; side to side - your 'setting triangles' are going to be huge by comparison. It's always safer to waste a bit of fabric for your setting triangles and have the need to trim vs not having enough fabric. Most times by the time you are finished sewing your rows together and getting your borders on, there really isn't an excess of much fabric at all in the setting triangles.
Good luck. If you like, post a link to your pattern or some photos and we might be able to give you some more hints/clues when your mind is a bit more fresh.