There is nothing wrong with making up Ramadan by fasting days separately
Question

A man has to make up the Ramadan fast. Is it permissible to fast the days separately?.
Praise be to Allah.Yes, it is permissible for him to make up the days separately, because Allah says (interpretation of the meaning): 
“and whoever is ill or on a journey, the same number [of days which one did not observe Sawm (fasts) must be made up] from other days” [al-Baqarah 2:185]. 
He did not stipulate that the days be made up consecutively. 
And Allah is the source of strength, May Allah send blessings and peace upon our Prophet Muhammad and his family and companions. End quote. 
Standing Committee for Academic Research and Issuing Fatwas