Is reading a daily portion of the Qur’an, a book by Sheikh Tantawi, and glorifying God (tasbih) considered sufficient for making good use of time, or not?

Time is a blessing that Allah swore by in the Quran, and a believer seizes their time for good. What you are doing — memorizing the Quran, reading books, and remembering Allah — is good. Your feeling of falling short is humility before Allah and a duty upon the believer, for even if a person spends their entire life in obedience, they are still falling short of what is due to their Lord. Islamic books can be obtained from multiple charitable organizations, and it is advisable to seek Islamic knowledge from its qualified scholars.