I assume you are in General Category and up to 1500 rank one can expect an interview call for MS Research. With new IITs this might go even lower. One more thing is for research admissions, at many places there might not be a GATE cutoff and based on resume - (CGPA in bachelors etc.) yu might be called as long as you have a valid GATE or other national level score. Even after this 1000s of students won't be getting a good college.
So, what constitute a good college? In my opinion it should increase the knowledge level and hence provide better career opportunities. IITs, select other institutes like TIFR, CMI, ISI, top IIITs are the nly ones in India which does this. Then there are insitutes which prvide good placements and top NITs are the ones to go for. Some professors at NITs do good research and for CSE NIT-Calicut is famous for this. If you get to any of the above colleges your career is safe.
Now comes some colleges which are good for B.Tech.and okay for M.Tech. due to placements. NSIT, DTU, CET Trivandrum, CEG Guindy, mid NITs etc. comes here. If you work "efficiently" - that is doing what is required for companies like Google, Amazon., Microsoft etc. you can get a good placement but there might not be much support from the college. The difference in these colleges and old IITs are that old IITs make you work really hard and hence you will be prepared for a better placement. Here, you have to do this on your own.
Now, below these colleges, at the level of low NITs, I personally do not recommend any one joining. Those people should have definitely written IIIT entrance, BITS entrance etc. Because after M.Tech. you might not even get a good job and you learn nothing. But you can devote time and prepare for GATE again and then get to PSU or other places depending on the work load.
Should I repeat? I have hardly said anyone to repeat. Usually those who successfully do repeat know this from their heirt and hence they do it successfully. If someone forces one to repeat he/she usually won't succeed. The only thing I can guarantee is that those who prepare in the proper way (I have told this in many posts- just browse through the blogs here) hardly fails to get a top rank. But for this, you should know the GATE syllabus well, and must have the commonsense to work for covering them all and not wait for someone to guide you. Whether you have coaching or not, you must guide yourself - can take help from seniors if needed. Then aim for scoring 80+ in the exam. This is possible and if you can do the needed, you can surely repeat.