Trouble summing

1 
select T.GrossValue,T.GrossValue + IsNull(sum(F.GrossValue), 0) as value from tblDWTicket T
   left join tblDWBookingFee F on T.Transnumber = F.Transnumber and T.CinemaCode= F.CinemaCode
  where t.CinemaCode=21 and T.transnumber = 10551105
  group by T.GrossValue,F.GrossValue,T.CinemaCode,T.TransNumber

I have an issue here.
select T.GrossValue from tblDWTicket T where t.CinemaCode=21 and T.transnumber = 10551105
this will give me:

GrossValue
3,75
6,50

select F.Grossvalue from tblDWBookingFee F where F.CinemaCode=21 and F.TransNumber = 10551105
This gives:
Grossvalue
1,00

Now the problem is that when I join in the first query, apparently the F.Grossvalue adds to both rows of the tblDWTicket so instead of getting
4,75
6,5
or
3,75
7,5
I get
4,75
7,5

I need to add this just one time and not two.
How can I do that?
Thanks