How much bigger are they?
You can trim your Pinwheel blocks down to whatever the UNFINISHED size of your plain blocks is......in this case, 5".
Having both sets of blocks the same size makes life so much easier.
Just make sure when squaring each block that you keep an eye on the diagonal and the center of the Pinwheel.
You want the ruler to have BOTH
a)the diagonal lined up so it bisects the corner exactly AND
b)the center of the block lined up with the correct measurement on the square ruler - for your block, 2.5"l.
You don't want to trim one side, turn it, and find out you don't have enough fabric, or that the Pinwheel is now off center (even though the diagonal is fine).
Both are equally important.
At least with using plain alternate blocks, you won't have all that bulk at the corners, your blocks should go together smoothly.