You can leave it out.

Generally put lemon in the strawberry is mainly to improve the gloss of strawberry sauce and neutralize the sweetness of the strawberry sauce, so that the taste of strawberry sauce becomes sweet and sour, because the lemon's taste is tart, add in the strawberry sauce can make strawberry sauce is not so greasy, but lemon is not a must ingredient of strawberry sauce, so when there is no lemon, it is also not necessary to put it, and will not have too much impact on the strawberry sauce. It's a good idea to add lemon to the strawberry sauce to make it less cloying.