Me and my girlfriend are trying to have sex and its not working out! help please!?

Me and my girlfriend have been dating for awhile now and we tried to have sex several times. whenever i try to go in i make sure she is wet and i am hard but i cant seem to get it in fast enough for me to stay hard.. we are both virgins and i know you have to use a lot of lube which we have not tried yet but can any of you give us some tips please? oh and also when i finger her i can get two fingers in but when i try to put my dick in it wont go because i try so hard that it doesnt stay soft!