Keep your thumb on the back of the neck, don't wrap it around so it comes onto your strings. I use index finger and pinkie; e.g. index finger on the D at A5 and pinkie on the D at G7. You may need to rock or bounce a little from index finger down fretting a note to pinkie down. Hope that helps!
Katlady, have you tried a short scale bass? Like the Fender Mustang which ‘Talking Heads’ bassist, Tina Weymouth used to great effect. If moneys an issue theres always the Squier VM Jaguar Short scale bass, Epiphones EB3 is another good short scaler
By the way, the octave of the note you are playing is two strings down and two frets up, e.g. E string 1st fret, ‘F’ and D string 3rd fret, ‘F’ one octave higher
If youre a begginer then you problably shouldnt worry. Youll be able to stretch your fingers more as you play more. I know guys whith tiny hands and they can play pretty well and reach the same notes as me on a 34
I'm going to give it a good go on the Fender for the time being and when I gain experience, I think, invest in another bass. Is there a particular make of Ibanez that has a narrower neck, or are they all on the slim side?