I don't really have any tips but Ava went from doing EXACTLY what yours is doing to suddenly pushing up and smiling and looking around. In a matter of days actually.

With her, I honestly think she could do it but hated it and so she refused to. Granted, she's a very very opinionated little thing. One day it's like she decided she found tummy time acceptable. This happened right at a month ago if I recall correctly. I even have pics showing it.

On 3/13 (3 months and 9 days old) this was one of her better moments with tummy time because we were using the Boppy pillow and she hated it even worse without it:

Taken the same day/tummy session, before she got ticked off:

This was literally all she could do it seemed and I was worried a lot about her upper body strength too but I just kept trying it for 5 or so minutes several times a day.

On 3/22, just 9 days later :

And by 3/31, she really enjoyed tummy time:

Love this one ^

I don't really have tips because it seemed like nothing worked and then suddenly it did, but I think I have an odd baby sometimes because lots of things are like that. The only helpful tip I could possibly share is to keep trying it because it is important. I thought Ava was going to be very behind but she rolled from her tummy to her back about the time she decided TT was okay (March 23rd to be exact) and then rolled from her back to her belly last week and this seems to be slightly early for back sleepers.

Good luck and hope this is at least encouraging for you, if not helpful