歩きすぎて、足の裏と足の指が痛いんだ。靴のサイズがあってないのかな。

、。。

I've walked so much my feet and toes hurt. Maybe my shoes aren't the right size.

Literal

Walk-too-much and, foot [gen-の] sole [and-と] foot [gen-の] finger [subject-が] painful-んだ. Shoes [gen-の] size [subject-が] not-matching [wonder-のかな].

Rich in colloquial pieces. (1) 歩きすぎて uses the compound ~すぎる ('too much') attached to a verb stem. (2) 足の指 literally 'foot fingers' is how Japanese names toes — the language doesn't distinguish 'finger' from 'toe' lexically, appending 足の for toes and 手の for fingers as needed. (3) サイズがあう ('the size matches') uses 合う ('match, fit'), here in the ~ていない form for 'is not fitting.' (4) ~のかな is the 'I wonder' speculation particle, combining の (explanatory) + か (question) + な (musing).