Hi Aspirant,

45-50 K rank is decent enough to get a government engineering college but not enough to get a good one.
1.By applying to JEE MAIN you may get one of the GFTIs or north-eastern NITs. In addition to this you may get lower branches of good NITS.
2.By applying to state engineering colleges, you can add a bunch of options to your list. States such as Gujrat, Madhya Pradesh, Punjab take admission through JEE MAIN Ranks though their separate counselling procedure.With your rank you would surely get a good government college.
3.You may also apply to central universities that take admission though their portal on the basis of JEE main ranks.Few of them are:

a.Hnbgu University, Uttrakhand
b.Silchar University
c.Ambedkar University, Lucknow
Your rank is decent enough to get into a college .By now the dates would have reached to deadline.You have to constantly check the dates.

Here is college predictor tool.

All the best !!