During college time there are almost no gaps between lectures and I find it hard to pray during such a short period of time which might mean "Kadaa al-Salah", so what can I do since I feel guilty for that?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Delaying a prayer from its fixed time is among the major sins. Allah Says (interpretation of meaning): {So woe unto those performers of Salât (prayers) (hypocrites), Who delay their Salât (prayer) from their stated fixed times,}[107:4-5]. Allah also Says (interpretation of meaning): {Then, there has succeeded them a posterity who have given up As-Salât (the prayers) [i.e. made their Salât (prayers) to be lost, either by not offering them or by not offering them perfectly or by not offering them in their proper fixed times, etc.] and have followed lusts. So they will be thrown in Hell.}[19:59].
Ibn Masoud (Radiya Allah Anhu) said that the meaning of "given up the prayers" performing the prayers after having passed their fixed times.
Being busy in study in a college or else is not a valid excuse to delay the prayers from their fixed prayers or to combine them.
Therefore, you have to return towards Allah repentant and perform the prayers on its fixed times even though there is no specific place for prayers.
Moreover, search for other Muslims to perform the prayers with them in congregation at any lecture hall or at any convenient place in university. If performing Prayers in congregation is not possible at the beginning of the fixed time you may perform at anytime during that time.
However, if performing the prayers in congregation is impossible, then you should perform it alone. Know that you do not have any valid reason to delay performing a prayer from its fixed time.
Allah knows best.