hey,

see your ability cannot be measured by how many percentage are you getting but also we cannot deny admission is being provided on the basis of marks as well , i understand you might be not well that's why secured low percentage , and now you are planning to for engineering see if you are having fine commands on science subjects irrespective of marks you have secured then go for engineering otherwise there is a big no from my side and as you have applied for JEE mains and in case you have qualified the same and going to take admission in any of IIT and NIT then they will ask for your percentages that is 75 percent you have necessarily secured thats why i guess you are not fulfilling

so i would suggest you if you want to go for engineering then opt any of the good private colleges

all the very best

'dont loose hope still you have chance to prove yourself!